In the 80's there was a big fuss about video nasties, all this talk about video games and violence is just the modern version of that. The truth is the people who are the most vocal on this subject often don't have a clue about video games. They complain about kids playing these games, but like movies games have age ratings, and so often should not even be playing them. They are made for adults and adults control who buys them, and should control what their kids play. If the entertainment industry only catered for the lowest age of viewer we'd all be watching baby programmes.
I don't think these games are nearly as realistic as some people try to make me believe, and I think that for these games to have the affect of making you more violent you have to be well down that road already.
What about books anyway, no one ever talks negatively about them. Your mind interprets the words and your imagination creates the scene, I think this gives more potential for triggering violence in people.