Games, along with any violent media, act as catalysts to the problems already present in our society, without directly causing the problems in most cases. However, the combined proliferation of violence by all sources can increase the number of problematic individuals, especially when children are exposed to all this violence. At the end of the day though, you can't keep violent games out of the hand of kids with bad parents, just as you can't keep guns out of the hands of people who want them (why gun control was even mentioned in this thread is beyond me). I live in Kentucky and know several hunters, so I'll hesitantly defend gun rights in most situations, but personally I don't enjoy super-violent games that much (haven't seriously played an FPS since SW Battlefront II). I don't see the need for games to be graphically violent to the extent that they are, especially when kids like several that I know are getting wrapped up in this culture of violence that I don't even see among the hunters I know.
I'd say that violent media in general (with games not really being different than movies/tv/rap/etc imo) serves as a contributor to these problems, but not a direct cause. We need to pull the weeds in our culture by the roots, not the stem. The problem there is that I can't really see a way to remove dangerous individuals directly, and that's why so many people try to identify tools of violence or background causes in the media as the problem. The real problem I see is that we've been raised in a culture with lots of unstable individuals, and most are trying to find some scapegoat instead of admitting that we're not as "civilized" as they would hope.
tl;dr= games are probably a little too violent, but it wouldn't be a problem if our culture wasn't so fucked up and inclined to violence already
Edit- realized something that seems important but doesn't change my view. Mortal kombat is probably one of the most violent games out there, but it doesn't get complained about nearly as much as the first person shooters. I think that's because the fps cause more problems due to trying so hard to simulate real violence, while mk is outlandishly, impossibly violent. So among the wide spectrum of violence in games, I think "murder-simulator" type, realistic violence is the main culprit of whatever problems violent games cause.