It's common enough to blame youth violent crime on the increasing popularity of violent video games. But the massive declines in violent crime since the emergence of realistic violent games suggests that, at minimum, games haven't caused more crime. And if anything, the opposite may be true. Erik Kain notes that large drops in the violent crimes have coincided with the rise of video game culture:

The fact that crime has been dropping for the past twenty years (along with things like teen pregnancy, etc. as I noted above) while more and more young people consume more and more video games should put a lie to the notion that video games actually increase crime and violence. I did a little Googling and found this paper by Adam Thierer [pdf] which doesn’t exactly support the idea that more video game consumption has directly contributed to less crime, but certainly suggests that it’s a possibility.

Kain also points to Gerald Jones's book Killing Monsters: Why Children Need Fantasy, Super Heroes, and Make-Believe, and suggests that video games may provide a sort of role-playing outlet for children to safely act out violent impulses:

 Maybe playing video games or getting into these role-playing situations where you can be the villain, the monster, the criminal, or even the hero, the special-ops troop, and so forth is an important way to develop another kind of empathy – an empathy with the person we could be or would like to be, or at least to explore that part of ourselves that we will never become – maybe so that we never become it.

I think you have to pair this idea with the multiple studies showing that access to pornography in specific and violent entertainment in general reduces the prevalence of rape. Violent entertainment seems to contain violent impulses, not unleash them. 

More on the effects of porn availability on rape from Steve Chapman here. Read Jacob Sullum on the Supreme Court's recent decision to strike down laws restricting the sale of violent games to minors here.