This story from NewScientist.com argues a point I've long believed must be true: doesn't engaging in such realistic simulations of savagery affect your response to it in real life?

...psychologist Bruce Bartholow from the University of Missouri-Columbia and colleagues have found that people who play violent video games show diminished brain responses to images of real-life violence, such as gun attacks, but not to other emotionally disturbing pictures, such as those of dead animals, or sick children. And the reduction in response is correlated with aggressive behaviour.