You probably do not live with someone who has a mental illness, someone who already has a skewed perception of reality.
Violent video games DO have an effect on these people. Of course, it is our parental responsibility to intercede in these instances.
Given that, not all people are identical, of course, and neither do people all react the same way to the same stimuli.
Once again, the realistic depictions of violence in movies are much more of a likely culprit than video games, wouldn't you think?