People who go off and shot up schools or muder others in real life due to "playing GTA or whatever game" are those who have some disorder mentally anyway or on drugs or social outcasts or from bad parental care (parents who don't care or teach values and respect). I've brought my kids up that games are for fun, none of its real "unless your going to be a space marine or a drugs lord", lol and its just pixels made up on a screen. TBH i find films far more disturbing and would'nt let him watch say Hostel or Saw because that is more visually real yet something like Aliens Vs Preditor - total made up and not real in my book would be fine. They know this, they know you cannot just go nick a car or beatup some person in the street and just get away with it, they been brought up to respect others.
They play games for fun as intended