I think it's only partially the kid's fault... there's a much bigger problem here. Parental influence (rather, the lack of), failing institutions (i.e. an unsupportive school system), etc.
All the violence seems like a cry for help and, even moreso, attention. Parents aren't spending any time with their kids anymore... nowadays, it's common for both parents to be off at work 8 hours a day, working their butts off because they want to give the best to their children. What they don't realize is, the best thing they could do isn't buy Johnny a brand new car or a new Tommy jacket, but spend some time just talking to him.
Here's an interesting statistic: nowadays, children spend more time watching TV during their first 6 years of life than they'll ever spend talking with their father.
Schools have gotten worse, too... social-scene wise, it's pretty bad (in terms of cliques, pressure, acceptance/rejection, etc.).
The rate at which there are school shootings nowadays is really disturbing... it's practically become a "normal" occurrance, which is just sick...