This was a 14-year-old. Any modern LSL game would be rated 18+. I'm not saying media influence isn't real (heck, I don't think i've ever wanted a big house until I watched Desperate Housewives), but that it can and should be managed to a degree.
That influence is only bad if he wouldn't have killed his mother if he hadn't played the game. Otherwise, it just influenced the means, which is more or less irrelevant.
If we apply the idea that game worlds should be moral, what about GTA?