Written in response to a wonderfully enabling message from Amanda, which contained many sources of inspiration (such as ruminations on where Kirk and Spock might jointly retire to after their Starfleet careers), but most especially prompted me to think about fraternization. She mentioned half-jokingly that Jim might perhaps feel uncomfortable hitting on his First Officer, and my first thought was, "Yeah, no." In Reboot, especially, Kirk is this rambunctious, instinctual, rolling ball (or balls?) of Id, like a large, playful and occasionally feral wolf in near-perpetual heat, largely uncontrollable unless you a) hit him until he passes out, b) jab him with a hypospray, c) choke him to near-death or d) exile him to a snow-ridden planet with giant man-eating beasts. Other potential deterrents and evasive maneuvers are no doubt extrapolated on in exquisite detail, in Spock's private logs, along with measures and counter-measures and legal loopholes in Starfleet protocol. You know they are.
That, and there's no way Jim will hesitate to hit on Spock if he doesn't hesitate to hit on Uhura, even after being awarded his captaincy - or on Spock and Uhura, depending on your preferences regarding subtextual threesomes. But let's not go there, because this is affirmatively and overwhelmingly a Kirk/Spock post. So.
Why Captain Kirk Can and Will Hit on His First Officer, or:
A Logical Discussion of Fraternization in the Context of Kirk/Spock, or:
Since when have such insipid things as rank and propriety ever affected the libido of one Jim Kirk? Never, that's what. I mean, how many times did he hit on Spock, on-screen, in TOS? And knowing what hand-touching signifies to Vulcans (YAY FANON), how often did he hold Spock's hands? Nobody, and I mean nobody, has ever touched Spock as much as Jim has. And perhaps more astonishingly, given Jim's general touchy-feely-ness, there's nobody that Jim's touched more than he's touched Spock, either. That's canonical fraternization, right there.
Starfleet's attitude towards fraternization has always fascinated me, not least because of intriguing instances (for example, in Voyager and Deep Space Nine) in which fraternization was not only widely accepted, but encouraged. Relationships between crew members were not only not frowned upon, but were celebrated with actual marriage ceremonies. Like, say, Paris and Torres in Voyager. They even had a baby. And a baby shower. That Seven of Nine did copious, painful and frankly embarrassing research for. Other canonical instances of Trek fraternization include Worf/Dax, Kira/Odo, Riker/Troi and... heck, I lose count.
So my guess is that non-coercive fraternization is actually A-okay with Starfleet, which isn't strictly a military organization, but it's only okay insofar as it definitely does not influence or bias command decisions, or enter into the creepy coercion category of things. And both Jim and Spock, I think, are far too serious about their jobs to let their mutual devotion put their ship at risk, and are also decent enough people not to pull rank on each other (except when one of them's being an idiot in a professional sense, in which case the other can find creative ways to bypass rank or pull it). And they don't hesitate in sending each other into danger, either. I mean - Spock and Kirk back each other up, sure, but they've also learned to live with the fact that the one they love can and will put themselves in danger on missions of import. It's the job. (That they both love.)
So, yeah. I think that given the lengthy durations of space missions and the relatively small number of people on-board sea-faring vessels and space stations, it is not surprising that Starfleet is somewhat more relaxed in matters relating to fraternization. It's still not explicitly condoned, but is probably accepted as a necessary non-evil. The unwritten rules have probably relaxed even more with time - conceivably, they were stricter during TOS than they were during subsequent series, because after sufficient time spent in space, Starfleet probably just had to throw up their hands (occasionally tentacles?) and admit that yes, their officers were gonna hop into each others' bunks. Because there were no other bunks. To hop into. Um.
Reboot is in the peculiar position of being the most contemporary (and therefore the most socially liberal) incarnation of Trek lore, and yet being a pseudo-throwback to those conservative times, before Starfleet was forced to admit that fraternization was perhaps unavoidable. So what happens with Jim and Spock now is still on the cards, really. Starfleet could go either way. Not that it matters, precisely, because neither Jim nor Spock are particularly good at following stupid rules and stupider authority figures (see: car-jumping and facing down the Vulcan Science Academy). If they love each other, they'll find a way to make it work. And damn the consequences.
If you ask most superior officers in Trekverse, they'll obviously say that they're morally bound not to take advantage of their subordinates, and thus would prefer to stay clear of fraternization within their own unit(s), but there are instances where a commanding officer and a strong-minded subordinate can have a non-coercive, functional relationship. In canon. (It's happened before.) It's not something that any decent commanding officer will enter into without being sure that they aren't pulling rank - but having a Vulcan as a partner? Pretty much removes the threat of the subordinate lying and saying that they're okay with it when they're not, or otherwise being physically weak enough to be intimidated. Yayness. More controlled, rigidly moral captains (like Picard and Janeway) would be less likely to enter into fraternization, anyway, as a matter of personal choice (and even they end up doing it!), but the one thing Jim is not? Is morally rigid. Rigid in certain other ways, though... Well, only Spock can testify to those. Ahem.
And the great thing about Reboot? Is that if there's ever any hint of Jim being dastardly enough to use rank to coerce his handsome First Officer into sexual relations, Spock will just have to choke a bitch. And that bitch will be Jim Kirk. The end.