Barret knows the others don't think of him as a thoughtful type, and to be honest they're not wrong. He's not thoughtful like Cloud or Vincent are, or even like Tifa is. He doesn't wonder about things much; what matters is what is, and what will be, not what might be, might have been, could have been, maybe, if . . . But he's alone a lot, when he's scouting for oilfields or coal deposits, alone with his own thoughts.
It isn't comfortable, because his thoughts tend to run themselves along two deep grooves, and it's hard to kick them back out even when there are more important things at hand. The first, of course, is Shinra. This is true even though Shinra is (mostly) toast, Rufus is (probably) dead, and the mako reactors are (most assuredly) out of commission. (He and Tifa took advantage of the chaos immediately after METEOR to make sure that they would be nearly impossible to put back in working order; restarting them would be near as much work as rebuilding them. He's glad they did, because even though Shinra's been lying low these last few months, he's seen blue-suit shadows in Edge, and that worries him.)
But even now that the substance of what he hated is gone, and only the shell remains—still he thinks about them. (So many gone, so much lost—he and Tifa lit candles for Biggs and Wedge and Jessie, in what had once been Aeris' church; the others never really knew them, and are sad only abstractly, but Tifa's cheeks were wet and he had felt the rising bubble of rage which was his mask for grief. They let the candles burn until they went out, smears of wax on a broken pew.) When he's in the city, he still takes a childish pleasure in defacing the Shinra logo, when he sees it. It's a private guilty pleasure that he keeps from Marlene. He doesn't want her to grow up learning hate from him.
That's why he's grateful that Marlene stays with Tifa while he's away. Tifa's got her broken spots, they all do, but her heart is huge.
. . . and that's the other thing he thinks about when he's driving, his truck bouncing and grumbling and threatening to overheat on the dusty plains: Marlene. In a way he did everything he did for her, because the rest of them might deserve what they get for sucking the life out of the Planet to power their lights and dishwashers—but she doesn't. She deserves a world that, if it's not perfect, at least works. She deserves the chance to make her own future. And that's all tied up in his hatred of Shinra, because the Shinras never believed that anyone had the right to make a future but themselves. Old Man Shinra and Rufus aren't all that much alike, but they're both supremely, teeth-grindingly confident, sure that their way is the way, and ready to destroy anyone who gets in their way.
And it's not fair for anyone, but it's especially not fair for Marlene, who is too small to fight back. She's too small to do anything when they bargain the future away for the present, then lock down the present tight as if it'd been hit with Break, so no one else can change what they wrought. She's too small to do anything about it, so Barret has to.
The others don't know this, but, gun-arm notwithstanding, Barret was never really meant to be a fighter. He was a miner, once upon a time, and a good one: he knows all about geology and refining and how to engineer a shaft so it won't fall in on your head. With the reactors down, and the Tower fallen, and Rufus (probably) dead (although the question of why one heard reports of Turk sightings, that still bothered him), building a future for Marlene meant doing that again, rather than fighting, and that was a small mercy in a broken world.
His phone rings. He answers it, hooking the phone between his shoulder and his ear. "Yeah?"
The connection is bad but it can't mask the warmth of Tifa's voice. "Hey. You busy?"
"Nah. Twenty miles outside Rocket Town. Still got thirty to go 'fore the first test site."
"Good. Someone wants to talk to you."
He knows who it's going to be even before he hears her voice, but he still smiles so big he's glad none of his assistants are around to witness it when he hears, "Papa!"
"Hey there," he says. "How're you?"
"We went to the market today," she says, her voice high and fast with excitement, "and I helped Tifa pick out a squash, and then she bought me maple candy."
"You bein' good?"
He smiles again at her exasperated tone. "Of course. I'm always good."
"Mostly," he agrees.