I agree, the M+17 rated games are truly awful at times. The only one I allow in the house are the Assassin's Creed games. Yes, they are bloody but it's not wanton killing for the sake of killing, at least the hero is truly killing bad guys. And there is a lot of history to be learned with those games, if you follow the story line.
I think what's worse is, like you implied, parents not really knowing what their kids are into. And therefore, not having a discussion with them about what's right and wrong. My husband is the one who plays the AC games, but my son watches him playing so we have