Games are games. Real life is real life. Anybody crazy enough to think doing something from a game in real life is ok, was crazy before they ever played the game and likely to commit some atrocity anyway.
Playing GTA does not make people kill people any more than playing smash bros makes people throw other people off cliffs. Torturing a virtual creature is not unethical because there is no creature. It is nothing more than electrical signals being redirected through microscopic switch boards. There is no intelligence, no pain, no feeling, no nothing.
Crazy is as crazy does. No amount of video games will 'desensitize' you into doing something you know is wrong.