People have no problems distinguishing between theather/movies/interactive movies (where faces are even better than in CoD)/games, and real life. And homicides (as well as other violent crimes) are going down for the last 20 years or more, while computer games are more and more popular.

It's quite clear to me, that violence in computer games doesn't make people more violent in real life. On the other hand it's possible that violent people do choose more violent games than less violent people.

Also, while we're on the subject of murdering people - easily accessible firearms do make people more likely to kill people. That's pretty low-hanging fruit right there.