I have had to do some research too on this topic for school... and there are as much researches which say that they are a bad ifluence and those who say bullcrapper..

there is so much info on this on the web so you can just choose a side and base your story on it as there is no definite answer for it..

Also many researches can by interperted in two ways.. there was one huge research being done which showed that people who played violent games, also had a higher percentage of people who commited crimes and such then people who didn't.. but this could also just show that violent people tend to play violent games