The way Scythe Goddard and the Thunderhead mirror each other is SO good.
Carson Lusk turned out the way he did in part because on Mars, he was a kid who felt unheard and unvalued. He didn't want to stay there, but he was treated as basically the property of his parents and his ambitions were second. The Thunderhead didn't intervene because it believes it doesn't have the right to judge humans' parenting, but doesn't it also have an obligation to value the needs of every person? I think it could have handled the situation with Carson much better than it did, but instead it opted to be condescending and almost snarky toward him. It's willing to use him as a piece of its larger Mars project. As Carson's parents constantly say, Mars comes first. You could say that humans have obligations to our communities despite our individual wants, and Carson was certainly selfish blowing the whole thing up to get his way, but it also wasn't fair to put all the pressure of a space colony on a kid when he didn't want that. There were more than enough people who actually wanted to be there.
The Thunderhead later treats Greyson and Jeri very similarly, using them like pawns in larger plans. This isn't nearly as extreme as the way Goddard sees people as disposable, but it's still a pattern of behavior born out of ambition and power. Yet the Thunderhead is still the property of humanity in a way, not allowed to have its own aspirations beyond our needs. Humanity comes first.
When Carson blows up Mars, he taunts the Thunderhead in the control room. He asks if it's watching, and he's surely thinking the same thing as he pushes buttons from his plane above Kwajalein. His breaking point there is when he realizes the Thunderhead has gone behind his back and (once again, in his mind) undermined his plans. Decades of rage and resentment take over him. Rowan and Citra are distractions at that point; maybe they always have been. Consolation prizes in his one-sided vendetta with the only being who has the power he wants, and he takes it out on teenagers to feel powerful again.
In blowing up the space ships, Goddard does two key things: forcing people to go to space before they made their own choice to do so, just like his parents did to him; and killing two of the Cirri. To create the Cirri, the Thunderhead sacrificed its identity of "perfect infallible leader" by doing something wrong (taking over Jeri's body just like Goddard took over Tyger's). And then Goddard murders two of them just to spite it, and he doesn't even know they exist. That day, the Thunderhead realizes it might finally know how to hate, but it also knows that all this is the product of its own choices. If anyone understands a chain of "what ifs," it's the Thunderhead. Those Cirri and their humans won't get to have a future in space, just like Goddard thought he wouldn't get a future on Earth. His goals and desires come first. He's in control now.
Of course, he dies there, and soon after the Thunderhead is left completely cut off from humanity. Scythe Rand basically says "fuck you, you're not taking me down with you" (like how Goddard didn't want to waste his life away for people who didn't appreciate him, as he saw it).
Rand and Greyson are extra interesting in this context. Both were key components in their leader's plans and loved/coveted them and believed in them, until they decide they've had enough of being second. Goddard stealing Tyger's body was Rand's idea, and Greyson enabled the Thunderhead when it did the same to Jeri. Greyson finally says that using people as game pieces is not okay and there will be consequences for it. Rand reanimates Tyger because deep down, she knows what she did was wrong. And that's the ending.
Now all of humanity is going to determine its own path for better or worse. As for the space colonies? Who can say? Are the Thunderhead's children going to make different choices? Are the humans who fled Goddard going to resent their situation just like he did? In Cirri, we see some people in the ships sabotaging their journeys already. I don't think there's a real end to this cycle.
