The Cultivation Theory talks about how people have choices. Yes, video games are violent, but we've all been taught right from wrong. The idea that people harm other people because of a video game is ludicrous.
Violence has always been apart of society, before video games and heavy metal. I do think that children are heavily influenced by what they see and hear though and should be shielded from that until they are at a much higher age.
When I was 13 years old I babysat for a friend of my mom's whose youngest was 4 and extremely difficult to handle. One of his favorite shows was The Power Rangers. I was never allowed to watch that show as a child because my mom always said it was too violent, at that point I could see where she was coming from.
He would jump on top of people, pull their hair and kick them in the stomach. It was always difficult to get him to settle down when he was trying to beat everybody up. Bandura published in his Social Learning Theory that children mimicked the violence they saw.
People are influenced everyday by things they see and hear. Video games are influential, but they don't take someone and turn them into a killer, that was something that was already inside the person. Children are the most affected by violence they see.