i so totally agree! my on has been violent at school and i found out recently that he was playing this violent game online. i believe this has something to do with his behavior.
i remember how my son played as bad cop and would shot me many times. he must have been imitated it from the video game he was playing. so yes i agree that it affect child's behavior.
be picky on what type of video games you allow your child to play and as much as possible stay on their side while playing so that you can explain on them what the game is all about.