When I was a kid the violent games started to release. You had games like Doom, Mortal Kombat and Time Killers. My father and I played all those games together, in the same way we watched movies like The Predator and Rambo. Watching Rambo is actually one of the first memories I have. The difference between my dad and most people's is that my dad is a hardass who constantly preached the difference between reality and fiction. He was and is still always telling people his views on what is real and just mere belief or fantasy.
The truth of the matter is that it's only entertainment. A child who can't tell the difference between fantasy and reality is a child whose parents let them down. My friends and I have played violent games since we were old enough to physically be able to play games and none of us are violent people, have criminal records or anything like that. Hell, I don't even have a speeding ticket on my record, despite the fact I've played through every edition of Gran Turismo except for 5 which will be finished soon.
Basically know your children (I would bet money the majority of parents don't truly) and teach them the difference between reality and fantasy and if they can't grasp it don't let them play mature games. Don't even bring them in the house. If they can, then the content in these games is really irrelevant. It will never be anything more than entertainment to them.
The ratings are there to let you know what the game contains so as a parent you can make an educated choice on whether to let your child play it or not. The law has gone as far as it should, imo. Make sure an adult is the person purchasing the mature rated game, same as tobacco and all that other jazz.