Here's a terrible experiment: try to rewrite Divergent with Peter as the hero. Here's the trailer we're thinking of:
There's heroic Peter, the brave bully, with his lifelong dream of hurting people. All he has are his friends Molly and Drew, who are so loyal that they're willing to dangle people over the chasm or bravely stab people's eyes out in the night to have his back. Helping Peter in his noble goal is Eric, the brave mentor who just wants to kill off all the Abnegation leaders so that Erudite can take over. (Is that so much to ask?) These four people will bravely stand up against Tris and her co-conspirators who want to stop Dauntless from launching a war on an unarmed opponent. Can Peter destroy Tris and save the city by killing a lot of people? Tune in to find out.
Yeah, that sounds like one bad movie. It's hard to make a heroic story out of a character whose main joy in life is being a big fat jerk. Seriously, from the moment Peter comes into the story, he's all about being awful. He:
• badmouths Abnegation (which seems like the future form of racism)
• refers to Tris by the derogatory term "Stiff" and even spray-paints her bed with the word (10.2)
• makes fun of Tris for being ugly, which might be fun to Peter and Molly and Drew, but isn't actually fun for anyone else
• yanks off Tris's towel when she's out of the shower (14.16)
Even if you wanted to write a version where Peter was the hero, it's hard to think of how to spin all that as awesome. And to top it all off, there's the time that Peter, Drew, and, sigh, Al dangle Tris over the chasm. Yeah, they say they're just trying to scare her, but after Peter (or one of his minions) stabbed Edward in the eye, do you really trust a word this guy says?
And so we're left pretty much believing Christina's read of these three:
"Peter is pure evil. When we were kids, he would pick fights with people from other factions and then, when an adult came to break it up, he'd cry and make up some story about how the other kid started it. And of course, they believed him, because we were Candor and we couldn't lie. Ha ha."
Christina wrinkles her nose and adds, "Drew is just his sidekick. I doubt he has an independent thought in his brain. And Molly... she's the kind of person who fries ants with a magnifying glass just to watch them flail around." (9.14-5)
Those paragraphs really lay it all out on the line. When it comes to these three, what you see is what you get. Christina starts with a thesis statement ("Peter is pure evil"), then gives an example of how he'd fight for no reason and manipulate people. That makes her argument pretty hard to refute.
Drew and Molly get less face-time here because they're less important villains. In fact, Drew is such an unimportant villain that he doesn't even have any moment of bullying Tris by himself. Molly gets two: making fun of Tris at the fence (11.65); and lying to the Erudite reporter about Tris (19.5). Whether these two are following Peter's lead, or are just plain awful in and of themselves remains pretty unimportant. Actions speak louder than words and in this case, their actions are pretty much the worst.
Sure, it's possible—maybe—that Peter, Molly, and Drew are all deep characters with feelings and complex reasons for their violence. But mostly they just seem like cartoonish villains. It's pretty easy to imagine Peter twirling his mustache while Molly and Drew stand cackling on either side of him.
Then again, maybe that's just because we see them from Tris's perspective. Maybe you could write this story with Peter as the hero. Maybe you could—but we can't.