While you are correct in saying that many of these games are DESIGNED for adults, they are often MARKETED to children.
I don't know, the gaming community as far as I see it is comprised of mostly adults. I'm not sure how rampant it is for youngsters to be playing games beyond their maturity level: maybe it is a problem. And even still, there's a bigger potential problem in an adult buying the game and letting a kid play it.
I'm not against violence in video games, even for young kids as long as it's tastefully done (as much of it is not).
It is the responsibility of parents and parents alone to control what games their children possess. As far as chat room access, it is very simple to restrict or prohibit access to chatrooms on your computer. Create log in identities with password protection, and prohibit your children from accessing websites with questionable material. This is blaming other people for bad parenting.