Say you watch a movie about rape and murder, no big deal, right? Then you watch someone do it in real life. Then you do it yourself. A video game is somewhere between the movie and doing the act yourself. Because you are acting it out in a virtual world. So anything in virtual reality is OK?
A video game is not real even if its a virtual world. Just because you shoot up a airport for example in modern warfare II does not mean you are not on the next step to being a mass murderer. Most people can diffrentiate between reality and a video game.