Miguel is Fine, Actually (Being Spider-Man's Just Toxic As Hell)
Before I watched ATSV I said that I would defend my man Miguel O'Hara's actions no matter what, because he's always valid and I support women's wrongs. I was joking, and I did not actually expect to start defending him on Tumblr.edu. But I'm seeing a lot of commentary that's super reductive, so I do want to bring up another perspective on his character.
Miguel wasn't acting against the spirit of Spider-Man, or what being Spider-Man means. Miguel isn't meant to represent the antithesis of Spider-Man. Miles is the antithesis of Spider-Man. Miguel represents Spider-Man taken to its extreme.
Think about Miguel's actions from his perspective. If you were a hero who genuinely, legitimately, 100%, no doubt about it, believed that somebody is going to make a selfish decision that will destroy an entire universe and put the entire multiverse at severe risk - if you had an over-burdened sense of responsibility and believed in doing the right thing no matter what - you would also chase down the kid and put him in baby jail to try and prevent it. He believed that he was saving the multiverse, and that Miles was putting it in danger for selfish reasons. Which is completely unforgivable to him, because selfishness is what he hates the most. And then he goes completely out of pocket and starts beefing with a 15yo lmfaooo he's such a dick.
But why did Miguel believe that? Why did he believe that Miles choosing himself and his own happiness over the well-being of others was the worst possible thing? Why did he believe that tragedy was inevitable in their lives, and that without tragedy Spider-Man can't exist?
Because he's Spider-Man.
Peter Parker was once a fifteen year old who chose his own happiness over protecting others. It was the greatest regret of his life and he never forgave himself. Peter's ethos means that he will put himself last every time, and that he will sacrifice anything and everything in his life - his relationships, his health, his future - to protecting and helping others. Peter dropped out of college because it interfered with Spider-Man. He destroyed his own future for Spider-Man. He ruins friendships and romantic relationships because Spider-Man was more important. If Peter ever tries to protect himself and his own happiness, then he's a bad person.
That is intrinsic to Peter. Peter would not be Peter without it. A story that is not defined by Peter's unhappiness is not a Spider-Man story. If Peter doesn't make himself miserable, then he's just not Peter.
That is a Spider-Man story: that not only is tragedy inevitable, that if you don't allow yourself to be defined by your tragedy then you're a bad person. If you don't suffer, then you're a bad person. If you ever put anything above Spider-Man, then you're killing Uncle Ben all over again. Miguel isn't the only one that believes this - as we saw, every Spider-Man buys into what he's saying. There's no Spider-Man without these beliefs.
Miguel attempted to find his own happiness, and he was punished in the most extreme way. He got Uncle Ben'd x10000. He tried to be happy, and it literally destroyed his entire universe. It's the Spider-narrative taken to the extreme. Of course Miguel believes all of this. Of course he believes this so firmly. He's Spider-Man. That's his story. And the one time Miguel tried to fight against that story, he was punished. And like any Spider-Man, he'll slavishly obey that narrative no matter the evil it creates and perpetuates. Because if he doesn't, the narrative will punish him. The narrative will always punish him. It's a Spider-Man story.
I don't think the universal constant between Spider-Mans, the thing that makes them Spider-Man, is tragedy. I think it's the fact that they never forgive themselves. And Miguel is what that viewpoint creates. He doesn't believe this things because he's an awful, mean person. He believes them because he's a hero. He's a good person who hates himself.
Across the Spider-verse isn't really a Spider-Man story. It's a story about Spider-Man stories. Miguel's right: if this was a Spider-Man story, then Miles acting selfishly really would destroy the universe. But Miles' story isn't interested in punishing him. It pushes back against Peter's narrative that unhappiness is inevitable and that you have to suffer to be a good person. It says that sometimes we do the right thing from love and not fear, and that Peter's way of thinking is ultimately super toxic and unhappy. ITSV was about Miles deciding that he didn't need to be Peter Parker, that all he needed to be was Miles, and ATSV is about how being Peter Parker isn't such a good thing. Miguel shows that. Whatever toxic and unhealthy beliefs he holds - they're the exact same beliefs that any Spider-Man holds. He's a dick, but I don't think he's any more awful a person than Peter is.
TL;DR: Miguel isn't a bad person, he just has Spider-Man brainrot.