The whole 'computer games make you violent' argument is, frankly, pish.
Every so often it'll hit the headlines, some halfwit will go on a rampage "after playing Grand Theft Auto" or some such. What these headline-grabbing knee-jerk stories fail to understand is this. Computer games, movies, TV shows, comic books, etc etc, do not make people violent. If they did, we'd all be doing it.
No, violent people are already violent. People who go on murderous killing sprees are wrong in the head. Games didn't cause that, they were messed up to start with. Sure, they might've just watched the latest horror movie before picking up a shotgun, but that doesn't imply a causal link. If that movie didn't exist, they'd have watched TV or listened to heavy metal or, hell, sat knitting for what difference it makes.
It's lazy journalism and wooly thinking. Too much knife crime? Let's ban knives. That'll work. Except, a) people who want to carry a knife for 'protection' are the kinds of people who will do so irrespective of the law, and b) if by some miracle we did stop people carrying knives, you'd see a decrease in knife crime and a commensurate increase in hammer crime, broken bottle crime, and half-brick in a sock crime. It misses the point, which is, this isn't knife crime, it's thug crime and what we need to be doing is apprehending / educating / punishing / rehabilitating aggressive thugs. Not looking for scapegoats and excuses.