As a mom, I do worry about some of these games. Especially when the kids get so hyper and want to spend hours at it. I only played once, at a pier video court. The screen was huge and the characters were life sized and life like. Even for me, my adrenalin was off the charts.
However, I don't see these games causing kids to become mass murderers. There is a whole combination of things that does that. Just look at the past several shooters. They all had mental problems, have social issues, on drugs or booze and probably were having delusional and/or psychotic episodes.
We really need to do a better job of identifying these people.