IMHO, I think the main problem is parents who don't do their job and teach kids right from wrong. The gradeschool I went to, I saw plenty of kids who were being "raised" by the disfunctional school system. Their parents didn't want to discipline them or teach them right from wrong, they either wanted to be their kids friends or they didn't want anything to do with their kid (go away son, ya bother me mentality).
The part of it that really shocked me was that after graduation I bumped into a kid who was a nasty bully. He apoligized for acting the way he did and also said that he was surprised that I never brought a gun to school and just started shooting. I was appalled to learn that he wasn't the only one who expected me to do such a thing! Hell, I never even entertained that thought as a daydream! The closest thing I came to thinking along those lines was the thought that an old schoolbuilding might be a fun place to play an indoor game of paintball. But bringing a real gun to school to shoot at people? That thought never crossed my mind, I was raised to see that as beyond pale.