I don't blame video games for violent behaviour. As I've said many times before, I blame bad parents and stupid kids. For starters, video games are much more carefully monitored now. It is against the law to sell a game to someone under the age rating, and many stores take this seriously. Hence why GAME and Gamestation are under administration (well, one of the reasons anyway). If I see a 12-year old holding Battlefield 3, I can tell you it's the parents who are to blame right away.
But that's just a stereotype, to some extent. Exposure to excessive violence can turn people into secret sadomasochists - the blood, torture, humiliation and screaming can do a lot to a young mind. And if it doesn't disturb them, it twists them.
Want proof? Check out a single paragraph from 8MM, starring Nicholas Cage "it doesn't exactly turn you on, but it doesn't exactly turn you off either". Let that set the tone for what you'll experience.