People with violent tendencies may do violent things based off of what they saw in video games. Luckily, those kinds of people are a minority.
Also, much of the fault of kid-gamer-turned-killers lies in the parents that are stupid enough to let their kid con them into buying them Grand Theft Auto. The ESRB, whose job is to put labels on a game to tell buyers what kind of content they have, are continually getting flak because of these dumbass parents.
"I'd also like to point out that if the game didn't have anything to do with Sonic at all, you'd say it's pretty good."
Blaze-Heatnix, on Sonic games