Regarding the "1%" argument, is it fair to assume that "1%" is shorthand "any chance at all"? If that is the case, I don't think it is unfathomable to hypothesize that banning violent movies, games and music might have a small chance at preventing an act of senseless violence. There are many psychologists who find that fantasizing about acts of violence is not a healthy way of dealing with stress or more serious mental ailments. Violent video games (as well as other violent media, depending on the context) are ostensibly violent fantasies.
Do I think violent media should be banned? No, we have a First Amendment to prevent that. I do think, however, people who enjoy violent games are quick to exonerate them of any negative social impact. It may sound callous in the wake of tragedy, but the violent media debate and the gun control debate are not necessarily about right and wrong. The question at the heart of both of them is: how much freedom do you want to give up for security? Every society must decide where they want to set that balance.