My gosh, ever since he's started playing those games hes gotten so rude. I knew they cause violence.
Actually video games don't cause violence at all. Here is the proof.
A peer-reviewed study published in the Journal of Adolescent Health found that children, especially boys, play video games as a means of managing their emotions: "61.9% of boys played to 'help me relax,' 47.8% because 'it helps me forget my problems,' and 45.4% because 'it helps me get my anger out."  Researchers point to the cathartic effect of video games as a possible reason for why higher game sales have been associated with lower crime rates.
There you have it, and that's just a taste of the evidence against video game related violence.