What I aim to do here is track what we see and connect pieces together. I will leave it to other people to do truly in-depth analysis that connects up to real-world things and turn up interesting ideas. It's also just going to be about the show canon, although I'll be considering book canon for clarity on some of the elements.
Let's start with the main character, Geralt, and Episode 1, The End's Beginning.
After a fight scene with a monster, Geralt enters a tavern and has a brief civil interaction with a barmaid, Isadora, only for her to be pushed aside by the tavern-owner who hates witchers enough to want him gone now, a sentiment echoed by a number of other men in the place.
It is, I think, worth mentioning that this does not appear to come from a place of fear:
"You don't give the orders around here, you mutant son of a bitch."
"Go. On your own or at the end of a rope, your choice."
And when Geralt turns as if to leave, the men make it clear that he doesn't even get that choice, they've decided on a lynching.
"Yeah, fuck that. Kill him with your bare hands if you have to."
"C'mon, Witcher. You're not scared of us, are ya? Show us what you've got."
"Witchers can't be trusted."
The anti-witcher sentiment is based on broader anti-human prejudice, not that witchers are legitimately frightening. If mankind fears that which is different, they don't fear it in the sense it's physically scary to them. These men expect him to back down (they mock him for being scared of them) and the final jab before Renfri steps in is that he can't be trusted. When accusing witchers of being no better than the monsters they hunt, they don't mean in the sense witchers are as likely to kill people, they mean that as non-humans their loyalties are suspect.
And it is probably not a coincidence that what we see is highly gendered. Even if we discount Renfri as having her own reasons, Isadora doesn't have any problem talking with him. And Marilka is probably not a good enough actor for all her enthusiastic prattling to be part of tricking him into visiting Stregobor. It's the men who are aggressive, likely because a witcher is doing a traditionally masculine role in killing very dangerous things the rest of the community couldn't and because he's just big and scary enough they think they can show off they're even tougher by harassing him.
Which is not to say that women necessarily disagree on him being inhuman. Marilka's chatter is heavy on other women:
"Isadora said you were looking for my father. She's a gossip, you see. Probably went two steps into the Lord's Inn before she was running off telling everyone an evil witcher had arrived."
Possibly this is putting words in Isadora's mouth because Marilka's heard elsewhere that witchers are evil, but if Marilka knows Isadora as a gossip, she's likely quite familiar with the sort of things Isadora says. Even people who are civil toward a witcher still believe them to be other. (As we will shortly see repeat with Stregobor.) That said, Marilka is wrong about what actually happened with Isadora (she didn't walk in, see him, and run out, as Marilka suggests, she spoke to him and only left after she was ordered to get away from him) and she still seems to have been helpful since she told Marilka that Geralt was looking for her father, which would've resolved the situation he was in.
"My mother says you're the offspring of foul sorcery, a diabolic creation, a filthy degenerate born of Hell."
Here we get the strongest statement against Geralt all episode. Again, the emphasis is not on what Geralt does or might do, but what he is. And this fits with how at episode's end, Geralt is going to kill most of the people initially trying to pick a fight without much effort and everyone is going to be shocked that the witcher they hated did a bad thing, because the prejudice against witchers has everything to do with what they are. From this, it seems like Geralt's tolerance for this sort of behavior is a standard trait of witchers. People do not expect violence from them and presumably behave this way to witchers regularly without consequence. Witchers must largely respond by either peacefully leaving or minimally defending themselves to make the other party back down.
Which brings up another issue - why doesn't Geralt just leave? What's he actually doing here? He seems invested in getting paid today despite not knowing if there's an applicable contract or not and running into a lot of pushback.
Geralt: "It's hard to make a living on main roads."
Renfri: "And you desperately need money for new clothes."
Marilka, shortly after: "That's enough to buy some new clothes. Just saying."
Geralt's behavior this episode is a bit unwitchery. He wandered around the wilderness looking for monsters of any kind then headed into the nearest town in case there was a reward. This does not seem like a particularly good business model, and what we'll mostly see for the rest of the show is people offering money first and then having a specific monster killed in return. Either Geralt is desperate for money so he decided to try to preemptively hunt a monster in the hopes of getting paid, or Geralt preemptively hunts monsters a lot and it's left him desperate for money.
On the one hand, the story Geralt tells Roach later about mistakenly thinking people needed him suggests he knows better than to do the latter... On the other, the story Geralt tells Roach is about him doing the latter. And the fact he's implying to Renfri that wandering around swamps just in case there's a monster is how he makes a living does suggest he does this a lot.
It is hard to say how representative Marilka is of the kind of interactions Geralt normally has, as not reacting much to events around him is Geralt's thing, but the fact that Marilka's friendly chatter involves a lot of objectively unusual things, like that she killed their dog, makes me guess it is probably not a common occurrence for Geralt. That said, again, people do not seem actually afraid of him, so kids finding him fascinating likely happens with some regularity. At the least, he doesn't appear thrown by Marilka's behavior.
We also get our first mention about the morality of monsters and monster-hunting from Marilka.
Geralt: "Your father, the alderman? He posted a flyer."
Marilka: "For a graveir. Kikimoras are useful. Population control."
and this will be echoed more forcibly by Stregobor shortly.
Geralt: "I kill monsters."
Stregobor: "The kikimora kills because it's hungry, Renfri kills for pleasure. She is a monster."
Now, this could mean it's a question the episode is asking Geralt, but by all appearances, Geralt unmoved by the idea that kikimoras should be left in peace to kill people and insists to the end that Renfri is not a monster. When talking about the story of his "first monster" he also has no qualifiers to suggest he's ever doubted his first evaluation.
I think what this is getting at is instead that witchers, despite being apparently mercenary, hunt monsters only by their own definition and not the definition of others. Geralt is unswayed by what non-monster-hunters think is a monster. He's the professional here. And he's also the one who has to live with what he does.
To go back to the tavern for a minute, there's another thing worth noting, which is his brief first conversation with Renfri. It runs pretty normally, which is actually incredibly weird going by all of Geralt's other conversations.
Renfri: "Want some breakfast?"
Geralt: "I'm full. Venison."
Renfri: "My mother, God rest her, would be mortified."
Geralt: "Our secret, then."
He's not particularly talkative, but he's volunteering information, responding to something that isn't a direct question, and making no effort to turn the conversation to what he needs to do next the way he does with Marilka.
Does he know Renfri's a mutant like he is? We'll learn in the third episode that Geralt has a ridiculously good nose, so, honestly it does seem like he should know. There's also the fact she's just stood up for him, which may make him consider her emotionally safe to be around even if he doesn't know yet she isn't a regular human (or, if she doesn't know herself, which is somewhat the same from his point of view).
On to Stregobor and the rest of what he says.
"I'd offer you my condolences, but I seem to remember that witchers don't feel anything."
This is the first time this is brought up and I really do think it's not a coincidence it's put in the mouth of the guy who murdered little kids because of a prophecy Geralt thinks is clearly bullshit. It does establish that both prejudice and general mystery about witchers goes beyond the random peasants. Even an acclaimed sorcerer does not really know much about witchers and you'll notice that he does not phrase this as a question but is completely fine assuming it's true. Geralt has a whole range of reasons to not respond to this, including in this case because he doesn't even want to be talking to the guy, so it's hard to pick out his feelings on people's insistence he has no feelings beyond a general dislike.
And yes, Geralt definitely dislikes. He's staring ahead during the conversation until he hears that witchers don't feel, then he turns to Stregobor.
If someone has a reaction to you telling them they don't care about anything, they care. He's also quite snippy with him after this point - he doesn't seem particularly a fan of the guy before this, so it's hard to be sure, but at bare minimum, Stregobor has definitely failed to endear himself.
Since we haven't seen much of other witchers, it's hard to say how much of this is about wanting to view witchers as alien and inhuman and how much is that Geralt's flat affect is a common trait among them. We do see in just this episode absolutely no one is actually trying to talk to witchers under the assumptions they're meat robots - both the people threatening Geralt in the tavern and Stregobor in the tower are acting as if he has emotions (Stregobor goes on at length about why Renfri needs to die and only mentions payment at the end, and is frustrated, not shocked, when Geralt refuses on the basis he only hunts actual monsters) and no one reacts with surprise when Geralt does show emotion. Geralt appears to be thought to lack feelings in the way one might saw a cow doesn't have feelings, that whatever his emotions are, they're different and so do not deserve any consideration. (It would be interesting seeing how people might react to a more conventionally emotional witcher - would visibly "human" emoting make people think they were an exception to the no-emotion rule, or would people still ignore it?)
Stregobor goes on to bring up DESTINY in the hopes this will help. It does not.
Stregobor: "I'm grateful destiny brought you to me."
Geralt: "Marilka brought me to you."
Stregobor: "Destiny has many faces, Witcher. Mine, for example, is beautiful on the outside, but hideous on the inside."
Stregobor: "And now she's tracked me here, just as you arrived. Destiny. Kill her."
Geralt does not reject this as vigorously as he does the prophecy, but he either ignores or contradicts when it's brought up.
Stregobor: "Killing Renfri is the lesser evil."
Geralt: "Evil is evil, Stregobor. Lesser, greater, middling it's all the same. I'm not judging you. I haven't only done good in my life either. But now, if I have to choose between one evil and another, then I prefer not to choose at all."
I think there's a lot to unpack here!
Geralt does not seem sympathetic to Stregobor in the conversation - he dismisses the prophecy ("Doesn't rhyme. All good predictions rhyme."), interrupts Stregobor explaining that these were evil monsters with "Innocent women are dead," and brings attention to Stregobor's self-contradicting claim that he knew the girls needed to be killed because he could tell from autopsying them. And there's how Stregobor keeps insisting they were inherently evil because they were mutants to the mutant he's demanding help from. Yet after all that, Geralt says he can't judge Stregobor because whatever his "haven't only done good in my life" is alluding to, he feels it's on the same order as murdering sixty kids over a fake prophecy with a dash of general prejudice. At this point there's no way to tell if this is his own self-loathing talking or if that he really did fuck up that badly. It's even possible that it's neither of those things and "I'm not judging you," is far more about Geralt never wanting to be put in the position of judge than anything else. After all, the entire episode hinges on Geralt trying to avoid choosing who should die.
But to be clear, Geralt's stance on the prophecy is "Innocent women are dead," followed by sarcasm. The question he spends the episode struggling with is absolutely not "Wait...was Stregobor right about killing kids?"
I've seen some talk about Geralt's rejection of the idea of a lesser evil being the real moral stance, and it's definitely part of one, but key to me is that Geralt, mid-episode, frames it in terms of his own wish to avoid making any choice. Not "it is right not to choose" but "I prefer not to choose". And because of it, by the end of the episode, he's been forced into a choice anyway, and one that I think fandom largely agrees was a less than ideal one.
Also key: Since Geralt does not believe in the prophecy, Stregobor is not actually advocating for a lesser evil as far as Geralt's concerned. And in this light, Stregobor's past "lesser evil" choice was, again, doing actual harm to avert a fake harm. Stregobor illustrates why settling for a "lesser evil" is so dangerous. Stregobor is even now telling Geralt that the horrible things he did were fine because it was at least a milli-Hitler less evil than another option he could imagine ("I admit what happened next was not ideal, but with the lives of Aridea's own children on the line, we had to act.") therefore join in on doing terrible things. That's the real problem with the lesser evil, that people settle for smaller rather than greater evil instead of striving to actually do something good and that people are, furthermore, absolutely garbage at actually weighing the two.
But Geralt is also not doing anything good here. At this point he probably thinks he doesn't have to - Stregobor wants to kill yet another person, Geralt can say no, nothing more happens because the prophecy isn't real and if Renfri does get into the tower, eh, nothing of value will be lost. (Geralt appears to be either willfully blind to the fact Stregobor will keep trying to kill her or extremely optimistic about the morals of whoever else Stregobor tries to hire. That said, if it's only a witcher who could take her down at this point, Geralt may be right in his evaluation.) But his refusal to judge Stregobor and determination to stay out of this, to settle for not doing evil rather than attempting to do good, will come back to bite him.
Having rejected Stregobor, Geralt leaves the town entirely. He's in the middle of collecting some plants by a stream when Renfri arrives, at which point he looks up and apparently decides that if he looks away again and acts really, really interested in leaves maybe she won't try to talk to him. Geralt is already pretty old by this point, so the fact he tries this suggests he actually has managed to wiggle out of conversations before by avoiding eye contact hard enough.
It definitely doesn't work on Renfri and she gives her own pitch. She knows he was told she's done terrible things, and she argues that she did them in response to what was done to her, therefore, take her side. The discussion with Stregobor is a decoy dilemma. Geralt had more difficulty extracting himself from the conversation than he did figuring out what he'd do. But Renfri... Renfri has a much more difficult pitch for Geralt.
Renfri: "Lilit help me, I will take down anyone in my way. Unless destiny intervenes."
Geralt: "You want me to kill Stregobor for you."
Renfri: "It's the lesser evil."
Renfi's argument is that Geralt should kill Stregobor because the man is going to die one way or another and Geralt can do it without collateral damage, while left to her own devices Renfri is going to try drowning the man in the blood of the innocent. This could have been made more clear, but it's why Renfri makes a distinction between her killing Stregobor and Geralt doing it. Otherwise, she'd just be trying to convince him to not get in the way.
Stregobor is easily dismissed by Geralt. "Kill someone, or she will kill me for trying to kill her," is not a choice he struggled with. But "Kill someone, or I will kill other people," is where the actual "lesser evil" question comes into play. Geralt is now in a trolley dilemma.
And Geralt, exactly like you'd expect someone who already tried to wiggle out of making a choice in the matter, tries to go for the third option of convincing the trolley driver to stop. What follows is a bit muddy.
Renfri: "People call you a monster too.
Geralt: "A mutant."
Renfri: "What if they come after you? Attack you?"
Geralt: "They have."
Renfri: "Why not kill them?"
Geralt: "Because then I am what they say I am."
In isolation, this exchange is "When people attack me, I do not fight back." This is...something of a hard sell. But Renfri has already been in a situation where she's attacked, fought back, and killed people. She opens the conversation confirming that she did kill the man who Stregobor first hired to kill her, as Stregobor claims, and she did more, as Stregobor claims, and gives her justification:
Renfi: "Stregobor's man raped me, robbed me and let me go." ... "I had to survive. I stole rather than starve. I killed rather than be killed."
If any of what Renfri did already was enough for Geralt to consider her a monster, they wouldn't be having this discussion. That said, for whatever reason Geralt does not volunteer any qualifiers about self-defense being different either.
We haven't actually seen how Geralt handles being personally attacked, unfortunately. While it's not clearly explained, Geralt, as a witcher, carries two swords and the silver one is for monsters while the steel one is for men, which pretty strongly implies that there is an awful lot of killing men in a witcher's life. He appears to have been willing to leave the town when it was a choice between "leave" and "be killed", but what was he planning when it turned into a choice between "be killed" or "be killed while trying to peacefully leave"? It seems hard to believe that Geralt could have survived this long with a rule that he can only kill people when he has some higher goal than his own survival, but on the other hand, he does have super reflexes, super healing, and his magic that lets him knock people back and block projectiles, so surviving the initial attack and fleeing may have worked for him. It's also possible his reception in Blaviken was exceptionally bad and we can put his apparent lack of surprise down to his poker face, but it'd be a weird decision to have the show introduce us to how people treat witchers with a completely unrepresentative situation.
The sanest interpretation, I'd say, is that there's a distinction between "attacked" and "about to die" - we see Geralt threatened in the beginning and respond nonviolently, and we see him getting stoned at the end and respond nonviolently (with the help of magic). This fits with how the context of the conversation is about revenge. Similarly, Renfri has just brought up a situation that was both "attacked" and "let live" where she feels she was wholly justified in killing - she specifies the first man let her go after raping her.
Geralt's reasoning really seems to boil down to that he fundamentally does not want to kill people - not wanting to kill people is the entire reason this episode is a moral dilemma. The act of killing people is monstrous, therefore he will avoid it whenever possible for his own sanity.
There's an argument to be made that this is Geralt is valuing his own life as lesser than a human's, but he clearly values Renfri's life to the point he does everything he can to disuade her even after killing her men. It would seem Geralt just doesn't see a contradiction between "your life has value" and "it's wrong to kill people who want you dead due to believing you're not human".
This is not really that coherent as a philosophy and it's not particularly surprising it fails to convince Renfri.
Renfri: "If I tell you, Witcher, that I can neither forgive Stregobor nor renounce my revenge, is that it? I admit I'm a monster?"
Geralt: "Yes. Or you can leave Blaviken and finally live. You choose, Princess."
Now, it's true that if she can forgive this, she's definitely not a monster. But that is not the minimum standard people are held to. It's not even a solution to her actual problem, because Stregobor wanted her dead for being born and showing him mercy now would not change his mind. Geralt is asking her to live her life forever looking over her shoulder for the next assassin. And she might survive like that - she's survived this long, after all - but it is a shitty, shitty thing to ask of someone.
And I do not think, in the overall context, that it's intended to be read as Geralt asking because on an impartial moral level this is correct. Rather, it's Geralt trying to duck out of a choice he absolutely does not want to make.
He can't undo any of the harm Stregobor did, and Stregobor is not in this moment doing more harm. Renfi is planning to introduce more harm into the equation, so if he can talk her out of that, he doesn't have to get involved. He's even convinced that this would be the best for Renfri - "you can leave Blaviken and finally live" - because not holding onto grudges (...or telling himself very hard that he isn't, at least) is how he's been handling things.
(An unexamined distinction here is that Renfri seems like she would also be able to go live her life after Stregobor is dead, while Geralt would have to wipe out a big chunk of the human population if he killed everyone with a grudge against witchers. Geralt's life philosophy comes from a place where what Renfri aims for is impossible for him.)
But by narrowing his vision to the immediate present and immediate actions, what he ends up doing is lobbing the problem back to Renfri. He states that if she does a thing, he will do a thing in response. There! Not his fault, right? Geralt's turned a thorny ethical situation into a simple one where he is just a sword that stabs monsters and doesn't stab non-monsters and none of this is a choice he's making because swords don't make choices, so whatever happens, Geralt definitely isn't going to be forever scarred by a choice he makes about this mess.
Unfortunately for Geralt, he doesn't actually believe it.
Because if this:
Renfri: "If I tell you, Witcher, that I can neither forgive Stregobor nor renounce my revenge, is that it? I admit I'm a monster?"
was all there was to it, the ending would be a simple victory of good over evil.
Geralt is contrasting Stregobor's "born evil" belief with the idea that what Renfri chooses will make her a monster. And that's very close to what he believes. But again, Renfri has already done a great deal of evil. Geralt could decide to quiz her on her past, on exactly how justified her various actions were, see if she's already disqualified herself. It's what Renfri expects of him.
"Here I am trying to convince you I'm not a monster."
But he's already decided. He refuses Stregobor immediately on the basis he only kills monsters, he only talks to Renfri at all because she sought him out, and he only knows what she's done and what her justification is because she volunteers the information. The other characters in the episode think this is a question of who's the monster, but the question Geralt's wrestling with is how does he handle situations more complicated than "this is a nonsapient animal that eats people and therefore you stab it".
Ultimatum that's also a bluff given, Geralt leaves, because again, his motive throughout the episode is to escape the entire situation. He sets up camp elsewhere and decides to unwind with a chat with his horse where he explains what proper witchering as he was taught it is.
What Vesemir would say, apparently: "Witchers shouldn't play at being white knights. We shouldn't try and uphold the law. We don't show off. We get paid in coin."
Now, Stregobor telling Geralt he'll get paid money for murdering Renfri doesn't violate any of those. Geralt isn't struggling with his decision to tell Stregobor to fuck off, though. It's the situation with Renfri.
To kill someone for the sake of their victim would be white-knighting, as would killing Renfri to prevent her from making more victims. Exactly what the legal status of what Stregobor did to Renfri is unclear but he hired someone to kill her and that's generally illegal, and Renfri is definitely a criminal about to kill more people. And it is, overall, a choice, instead of being as unobtrusive as possible and just doing what he's paid to do.
("We shouldn't try and uphold the law," though, is particularly sad. Discouraging witchers from trying to be their own law makes sense, but here we get an idea of just how apart from society they are.)
And he tells his horse about his first monster, which involved violating all of those.
"Want to hear about my first monster? Wasn't 50 miles outside of Kaer Morhen. He was huge. Stinking. Bald head. Rotten teeth. He pulled that girl from the cart, tore her dress off in front of her father and said, 'It's time you met a real man.' I told him it was time he met one too. It took two strikes to kill him. They weren't clean. But they were spectacular. I turned to that girl afterwards. She was drenched in the man's blood. She took one look at me, screamed, vomited, and passed out. Yeah. I thought the world needed me too."
Now, you can, and apparently people have, read that as him lamenting he wasn't rewarded with sex for heroism, but I am pretty sure that was not really the issue. "I thought the world needed me," he says, not "wanted me". What he wanted was to do good.
This story establishes some important things, though:
Geralt is actually really bad at not getting involved.
Geralt had and still has absolutely no issue with classifying humans as "monsters".
Geralt's (bloody) attempts to do good have had unintended and negative consequences to the point he expects that outcome.
Also, that he's reminiscing about killing a rapist right after Renfri says her first kill was her rapist should probably be taken into consideration.
And then we get the exchange:
Renfri: "Who were you talking to?"
Geralt: "I talk to my horse."
Renfri: "That's sad."
Geralt: "Is it?"
I would like to submit for your consideration that Geralt has enhanced senses. Did he actually miss that Renfri was right there? Possibly she has a super stealth ability but more likely Geralt either really doesn't see anything weird about chatting with Roach or he's past the point of caring. (Geralt's definitely grumpy when she asks who he's talking to, but he's so broadly grouchy that could be for a number of reasons.)
Or, of course, he meant for her to overhear that story in particular, but it does seem like he's capable of telling the story directly if he wanted. Renfri managed to tell him her own traumatic backstory without pretending she talks to trees and he managed to hold his side of the conversation then just fine.
Either way, yes, Geralt is definitely incredibly lonely and definitely talks to his horse all the time. We've just seen how badly a visit to a village went and the story even specifies the girl screams and vomits when he turns so she can see his face. And as fun as the hm/fuck meme is, Geralt does talk, sometimes elaborately. He just doesn't converse very well, exactly like you'd expect someone who's largely been making speeches to a horse. This also matches up well with how Geralt's response to other people trying to have conversations with him earlier in the episode has involved complaining about the other person talking to him:
Marilka: "You don't scare me."
Geralt: "That's too bad."
Stregobor: "She has stretched her bloody talons towards me."
Geralt: "Wizards are all the same. You talk nonsense while making wise and meaningful faces. Speak normally."
(Both those people also cheerily reminded him that human society does not consider him a member of it in the middle of the conversation. That's what you risk when you let other people talk instead of sticking to horses.)
At any rate, Renfri, the only person whose presence Geralt hasn't vocally objected to, is here to check in about if he's changed his mind on anything...
Renfri: "Tell me, Witcher. You don't believe in destiny or the lesser evil. What do you believe in?"
Geralt: "You mean who do I believe. I don't pick sides."
Renfri: "You just kill monsters."
And Geralt reiterates his position and his lies. As I said earlier, Geralt picks a side very early on. He just thinks he can make it not count by refusing to act. (It's also debatable if he "doesn't believe" in destiny or if he believes it exists but disagrees with the idea it's a moral force.)
Renfri says that in that case, she's taken his advice and threat, mostly the threat, seriously. She'll leave peacefully.
She then starts talking about her mother (the one whose broach she had, which in turn she used the first time she killed someone) and childhood, touches Geralt's leg, doesn't get stabbed, doesn't stab him, and after a bit of edging toward each other to see if one of them's going to change their mind about pulling out a knife, they manage to kiss. We cut away for discretion. Then we cut back, because it's on Netflix.
So, to recap Geralt's day:
Killed a random monster.
Went into town, almost got lynched.
Got chatted up by a stabby child.
Visited a wizard tower with 24/7 3D porn running.
Asked to murder somebody.
Asked to murder somebody take two.
Threatened to kill someone.
Had sex with her.
Still has made zero (0) coin.
Renfri, in the middle of sex, starts prophesying. Presumably this only happened in his dream version of sex with her, but I guess it's possible he had to sleep on it before he realized something was weird about that. Not important, though! What's important is this is a legitimate prophecy, and one of the things said is:
"You say you can't choose, but you had to. And you'll never know if you were right."
Geralt claimed that if Renfri killed people to get her revenge, she'd be a monster. That this was her choice, not his. That after that point, it'd just be him doing his job. But not only will he be obviously distressed about it throughout, the objective narrative voice of destiny itself is here to say that he does not ever get over this.
While Geralt is waking up from apparently just sleeping on the bare ground (and with his pan still out by the fire) Renfri's going ahead with her plan of killing people to get revenge.
And so Geralt is forced to do something. He had a choice earlier and he thought he was very clever outwitting this attempt to involve him by picking Option 3: remind everyone that he's a witcher, not a hitman, and refuse to do anything, hoping without him nothing can happen. And because of that, he now faces a different and worse choice.
Geralt heads to the market, unarmored and carrying his steel sword without a scabbord. He asks where Renfri is, then kills Renfri's men without saying another word to them. This does not resolve the question of what Geralt does when faced with lethal force because Geralt is killing people to stop them from massacring other people with his own survival necessary for that.
Then Renfri shows up with her sword at Marilka's neck to see he's killed them all.
Renfri: "You chose."
He did! And without any of the hesitation that's characterized this up to this point.
But he's still desperate to dodge the actual moral choice of the episode, which is what to do when someone has very good reason to be doing very terrible things. Renfri's men do not have the excuse of Renfri's personal trauma, and while you could argue they're helping out because they agree what happened to her was wrong, that they tried to pick a fight just because at the opening of the episode and how they generally do not seem to be conflicted in the slightest suggest that probably, they're just awful people.
But Renfri? The terrible thing she's doing is for a reason. So Geralt still wants Renfri to leave alive, despite his claim that she'd be a monster if she did this. Unfortunately, Renfri either sincerely believes she can singlehandedly kill the town if Geralt will just get out of her way or doesn't care anymore if she'll survive the attempt:
"I will kill her. I will kill everyone here until Stregobor comes down."
He tells her to leave. He tries to use magic to make her obey when he tells her leave. As I said, he was lying earlier. By all appearances Geralt does believe evil is a choice, but it's a choice you keep making. If someone stops doing monstrous things they stop being a monster. All Renfri has to do is stop, and even if she's made to stop by temporary mind-altering magic, that's apparently good enough.
There is certainly a kindness to this belief, and perhaps that's the main reason Geralt holds to it. But this kind of moral system is probably also a great comfort if you feel you've done terrible things, as Geralt alludes to in his speech about not picking any evil, and it smooths out your interactions with broader human society if when you encounter people who've done terrible things, like Stregobor, you can say that as long as they're not currently engaged in doing such it's not your affair.
At any rate, it doesn't work. As Stregobor told Geralt, she's resistant to magic, something impossible for a human, unless they're a mutant. The confirmation of one of Stregobor's claims about Renfri being different does nothing to change Geralt's mind because again, he just does not believe the prophecy means anything and witchers in particular are living proof that that "mutant" is not interchangable with "monster". Renfri rejects Geralt's continued attempts at an olive branch and picks suicide by Geralt. Geralt still tries to get her to surrender. Renfri refuses and continues however hopeless it gets. He kills her.
This is not what Geralt wanted to happen, and the prophecy makes it clear he does not consider it definitely the best option. Worth considering is that Geralt had enough choices throughout this episode that it's ambiguous if "You say you can't choose, but you had to. And you'll never know if you were right," is only talking about the final situation he ended up in or the situation as a whole.
Geralt does attempt to make a choice immediately afterward. When Stregobor shows up to collect his corpse prize, Geralt threatens to kill him if he touches the body. Even after she was given every chance to turn away from what she was planning and didn't take it, and even though she died in the process of it and so can never make the right choice now, Geralt insists to the very last that Renfri was not a monster.
Stregobor responds by turning the town against him in a scene that is either very weirdly compressed or is the guy actually using magic to manipulate the crowd.
"Witcher. You butchered bodies in the streets of Blaviken. You took the law into your own hands. You made a choice. And you'll never know if it was the right one."
(Although we won't learn this until a later episode, sorcerers can read minds. Stregobor's words are oddly well aimed at precisely what Geralt's weakest points are and require a much better insight into Geralt than he showed at any other point in the episode, so I think that may be what's going on here.)
In response to this, a screaming crowd trying to stone him, and Marilka, who he just saved the life of and who knows exactly what really happened, saying, "Get out of Blaviken, Geralt. Don't ever come back," Geralt's nerve breaks and he leaves.
Just leaves. Instead of, say, capping off the murder with killing Stregobor (it's not like there's consequences for killing one more person at this point) or at least taking Renfri's body with him, since it's clear no one could actually stop him. But Geralt's absolute fuck-up of an ending fits with the entire mess. He spends all episode insisting he shouldn't make a choice, then he finally makes a choice and it's terrible, so of course he ends where he begins.
He does take her broach with him, though, presumably as a reminder in case he ever stops being miserable for two consecutive seconds. He puts it on the hilt of his steel sword.
So, from this episode:
People's behavior toward witchers is based on xenophobia. That they're physically capable in a fight is, if anything, a mitigating factor, not the reason for it. There is a cultural belief that witchers are inhuman, but we only see men actually doing things based on that. It's hard to tell if the women are less invested or just more fearful of provoking them.
While this episode leaves some very lasting marks on Geralt, the events of the episode happen because some even earlier traumatic event(s) left Geralt convinced that faced with people talking about lesser evils he should run in the opposite direction. Geralt absolutely picks a side in the situation, he just doesn't want to act on it. I would say that not just the third episode but the events of the all of the next seven episodes, where Geralt just keeps getting involved, may be from how badly trying to chose nothing blew up in his face.
Stregobor seems more positive toward witchers than the townspeople and is certainly better educated but still mentions witchers having no emotions, so that appears to be a nigh-universal belief. No one seems to literally think they're emotionless and instead it means something more like "witchers don't have real person emotions like me". Geralt also has at least enough of a grasp on his own emotions to know people are being assholes when they say he has none.
Geralt absolutely doesn't believe in the Black Sun prophecy. Whether or not Renfri was a mutant doesn't change this, and whether or not all the girls were mutants doesn't change this.
While he's very good at killing humans, we have no evidence so far he'd do so for himself rather than others. That said, one of his two swords is for killing humans and that's standard for witchers, so whether it's for others or for themselves, evidently they find themselves needing to kill humans a lot.
Geralt hates killing people. He does not define "people" as having to do with how far you are from "human" and he does not see "human" and "monster" as mutually exclusive terms.
Also, he's actually quite firm on his definition of monsters - the episode isn't actually him wrestling with the question of if Renfri's a monster. He goes into this saying they were all innocent and his final act is taking the broach Renfri inherited from her mother (who loved her and did not think her a monster, it's the stepmother who wanted her dead), which Renfri used to murder a man in revenge rather than self-defense, and he'll place it on the steel sword that's for non-monsters.
While people misinterpreting what happened and screaming he's evil is surely upsetting, the primary traumatic event here is Renfri's death and Geralt's involvement in it. What will haunt him is "You say you can't choose, but you had to. And you'll never know if you were right," not that "Your reward will be a stoning." I would go so far as to argue that the biggest impact of that rejection and isolation is that Geralt is left with no one to confide in about what just happened. He has only his own sense of right and wrong to guide him, and he wasn't comfortable with that even before this happened.