there is speculation that those games desensitize people. but i'd think it would only be an issue with someone who is already unstable.
which brings us back to the mental illness issue.
It isn't just video games though. For a long time gratuitous graphic violence has been available without restrictions of any kind for kids as young as PG13 in the movies and on televsion and even Disney movies for the youngest have more graphic violence than was once socially acceptable. Kids are plenty smart enough to differentiate between the violence in say the Elmer Fudd/Bugs Bunny cartoons or the Coyote and the Roadrunner.
But can they mentally separate out the violence they see in Batman, Spiderman, Superman movies? Song lyrics, especially rap, is full of some of the most unconscionable violence and nobody even blinks any more. Our language has become more coarse, insulting, graphic, and suggestive. We are in a culture in which chidlren who were once taught respect, civility, and courtesy for their elders, most especially those in authority, to a litigious culture in which such values are now held mostly in contempt and lashing out in anger to punish those who 'offend' us is not only the norm, but encouraged.
Amd as we become a society more and more desensitized to violence, blood, pain, and cruelty and righteous retaliation, add in mind altering drugs and a sense of entitlement and I think it makes for a very volatile mix, most especially in those who are irrationally angry and via mental illness or drug induced, mentally unstable.