It's called alienation. In our culture, the fetishization of commodities and material wealth has given our society a very impersonal, dog-eat-dog attitude. This, combined with the traditional expectation that men are not to share their emotions, is a recipe for an atomized society, with people growing ever more distant from each other as they seek to get rid of their negative emotions through the media and the accumulation of material goods. Of course, these things don't bring true emotional fulfillment, so it's no wonder we've got angsty teens monstruous enough to slaughter classmates without feeling bad about it. They don't feel that they have purpose in their lives, or that they belong to a community that cares about them, or that the experience called life is so magnificent that to deprive others of it is the worst thing anybody can do.

It clearly cannot be drugs, or violent video games, or metal music, that drives teenage boys to such heinous acts, although many like to blame it on such things. Really, the cause must be a deep-seated psychological feeling of emptiness and alienation, and we have to ask what we can change about our society to prevent that kind of thing from happening.