Playing violent video games does NOT cause violence. In fact, most people who play violent video games do not commit violent acts. The same goes for violent movies and tv shows.
As it stands, the entire argument for banning violent videogames is based on one huge "post hoc, ergo propter hoc" fallacy; if a kid played a violent video game and went and shot someone, causation is derived from those events by clueless people, even when there is no information available that implies causation.

Only with research will we understand it, but instead of people pouring their lobbying dollars into research to find the real truth, they bribe Congress instead.