I think it's really got to be down to the individual, and their perception of / reaction to the games. Games are now rated according to their content, and as such parents and shop owners should be more responsible when allowing people access to these games.
Personally, I love video games, including the violent / horror games. It's an escape for me, but one I can switch off from when I come back into reality.
I think it's possible that if there are already underlying mental issues (discovered or not), they can be aggravated by these games. But whose responsibility is it overall ?
If they take them off the shelves, people will cry out "it's censorship". They have put warnings and age ratings on them, people are saying "It's not enough".
As regards demons, that's a stock WTBTS response to almost anything that they frown upon.
They say get rid of doom 3 - I'd say find some better band members!!
Bull!