I think it's used as a scapegoat for bad parenting. If the child is unstable, and comes from an unstable home - then yes, violent video games are only going to add fuel to the fire. The real problem, however, was there already. What some people who claim that video game violence has a significant impact on children don't realize is that aggression in children cannot be attributed to one autonomous factor. It's very much a combination of several... and video games/Marilyn Manson music, etc often take most of the hits when in reality, aggression is far more deeper than a stupid game or a song.
For the rest of us who have a good head on our shoulders, I don't see why it's a problem. ****, I've been playing RE since I was 8 or 9, and I'm pretty sure I turned out fine. Had I had negligent parents, it probably would have been different.
Not to say that everything is attributable to poor parenting though. The Columbine killers, Eric Harris and Dylan Klebold seemingly had great parents. The media pointed to 'Doom' as the reason for why it happened, but I just think it's so superficial to look at one cause and say 'aha! That's why!'. I don't think it's that cut and dry.