I agree with pretty much what everyone says. It's a matter of personal conviction.
For some people, when they play a game like CoD, Assassin's Creed, etc., they may get the influence and urge to take up the reality of what they play. In this particular situation, I would say yes it should be something they should limit/cutoff, if it's as bad as they are saying that it is.
For other people, the intensity of the game could be crazy, but when they get off they know the difference in reality and in fantasy, I don't see any problem with them playing it.
It's all in a matter of personal perspective.
For me, personally, I don't play a lot of shooting games that often mainly because of the realistic influence it can have on me, and parts of my past that I'm not exactly the most proud of. Because of this, I know that if I do play any FPS games that I need to be sure and limit what game I play and how long I play it.
Hope this help!!!