In 2005, The Lancet published a comprehensive review of the literature on media violence to date. The bottom line: The weight of the studies supports the position that exposure to media violence leads to aggression, desensitization toward violence and lack of sympathy for victims of violence, particularly in children.

In fact the surgeon general, the National Institute of Mental Health and multiple professional organizations — including the American Medical Association, the American Psychiatric Association and the American Psychological Association — all consider media violence exposure a risk factor for actual violence.

To be fair, some question whether the correlations are significant enough to justify considering media violence a substantial public health issue. And violent behavior is a complex issue with a host of other risk factors.

But although exposure to violent media isn’t the only or even the strongest risk factor for violence, it’s more easily modified than other risk factors (like being male or having a low socioeconomic status or low I.Q.).

— Does Media Violence Lead to the Real Thing? – NYTimes.com