It is correct that violent content, playing or watching, can affect your behaviour... but...
Let's take a game "condemned: criminal origins". The game is psychological thriller, with very brutal violence and very dark and scary atmosphere. You enter room and hear noise. You see dark figure running in next room. You shoot but miss. You check the ammo: no ammo! Damn. You drop your gun and grap the pipe running at wall. Right at the moment, a drug addict runs at you, swinging locker doorBANG! Ouch. You take it back and swing the pipe at the thugs face, giving the guy horrible scream, blood splatting over the walls and teeth flying on floor (and with the voice effects). The addict curses and makes counterattack, but misses. You swing the Canalis Analis couple more times and make him unconcious. While unconcious, you take the thugs head and bang it to your own, with very stomach twisting crack. Im thinking: jesus, this game is *dirty word* awesome!
BUT
It still doesn't make me bloodfrenzied killer. I actually sold my knife collection last week, and felt huge relief. I have also chosen non-military career in country where it is almost required (and respected by most). Im very peaceloving person and I will avoid violence by all means. I believe in self defence however..
BUT
Some of us snap. And then, the mr. and mrs. perfect comes and blames the videogames. Simple. And usually blames games like doom or mortal kombat, that are the most favored games of teenagers. Bwahhahahah!