I think in order for violent games to affect someone in the way many people seem to be implying, that person would have to already have something of an unstable personality, an inability to see where the dividing line between fantasy and reality lies, or a disconnect between themselves and the world around them. People have a tendency to assign blame to the visible, external factors (most recently to video games, although TV/Movies, RPGs and even music has taken the blame before) without paying any attention to the internal, personal problems which caused the issue in the first place.