America's aggressive "fuck everyone else" cultural attitudes are focused and condensed by the drama filled subculture of schools. Combine with the stress of increasingly shitty teachers and lots of boring school work stemming from a lack of interest by school boards to make work enjoyable, and you have a recipe for a shit school life.

Then they wonder why once in a while someone snaps and goes postal. Must be law-abiding grown-ups with firearms. That's definitely it.