This discussion is and will always be moot. Mostly, because the logic behind it has been disproven and largely debunked by the scientific community. In spite of that, people constantly have been using the same arguments for video games being a direct cause of violence. So I can't help but feel a little frustrated about how ignorant this thread sounds.
I'm sure it makes absolute sense: a person watches violence, hears about violence and participate in violence(well, sort of, in a video game), ergo he is violent. That is what sociologists and communications scholars call the Powerful Effects Theory or the hypodermic needle model.
The Theory contends that like a hypodermic needle that injects drugs directly into a blood stream, media content has a direct and immediate effect on consumers of the content.
The basis for this Theory is The War of the Worlds 1938 Radio Drama that was performed by Orson Welles. You can find easily find out the details of what happened on Wikipedia. But the short version of it is, he read War of the Worlds on radio, and people starting freaking out because theyactually believed that it was an actual news report and that aliens are really invading Earth (oh, those silly people in the 30s!).
But the Theory has since be debunked and replaced by other media theories. Research has shown that the media (in our case video games) are not as powerful as we think it to be. Our behavior may be influenced to some extent by the media, but we are more likely to influenced by our cultural and familial background, the friends and people whom we associate with, the kind of education we received, our life experiences, etc, etc.
So in short, video games are not the main cause of violence. Period.
