Cracked.com says something really smart.
This was brought to my attention by kane_magus. It's from Cracked, so it has some profanity and some off-color humor, but I think it pretty much mirrors what my thinking has been on this matter for many years.
The article: "The Truth About Guns and Video Games"
The long and short of it is this: Yes, video games are a part of our culture of violence. Yes, video games are becoming more violent. No, video games do not cause people to act violently. Violent video games are a symptom of the problem, not the origin. American culture is already violent, because we glorify violence. This leads us to consume music, movies, and games that glorify it further, not the other way around.