Not sure what your school experience was like, but for me it wasn't a bunch of equally intelligent students all thinking themselves above average. I'm happy to be in a career now where I feel surrounded by people who make me feel stupid; back then, it was very different. In high school, I never got less than an A with minimal effort, while everyone around me struggled. I don't say that to brag--I was just a big fish in a small pond. It's quite rare that many smart people are all clustered together, especially in a US public school in a relatively poor region.
Yes. And there are also narcissists who believe they are so special, normal rules don't apply to them. And when I read the manifesto as a whole, I get that vibe more then then the smart bored kid vibe.
I mean in all seriousness, it was not learning nor existing without skin color, without nationality, without religious bias why "they called us criminals".