Nobody can ever really say if they affect a person or not. Personally, a close friend of mine is addicted to video gaming in general, and many of his games are gory and/or violent, yet he can't stand either in reality. Recently, however, he's been developing into a more violent person and is beginning to show a fierce dislike of most women in general (unsure why - he's 15, normally guys are all over girls at that age) and is extremely racist. How racist? I went to a movie with him once - Snakes on a Plane, if you must know. Throughout the entire duration of the movie, he was throwing popcorn at some seikh family infront of us, directly aiming at their turbans and finding it highly hilarious.
I dont know if this is a development of his own character which would of been the same had he not been exposed to violent video games/movies, but I somewhat doubt it. When I knew him in grade 3-4, he was quiet, reclusive and shy. Such a startling change in only 4 years concerns me.
The majority of the games I play personally are somewhat violent and/or extremely violent at times. Counter-Strike, for example. Half-Life 2 may count, not quite sure if that fits under violent or extremely disturbing (
) and World of Warcraft. All contain excessive amounts of violence, yet I am a pacifist by nature in reality, and I haven't laid a fist on someone in over 7 years. I intend to keep it that way.
Final conclusion? I believe violent video games and movies can have an effect on some people, but not the majority. The media abuses this to no end, and have successfully established a stereotype among the computer-illiterate people about us otaku folk.