This is a very hard subject to debate, and honestly it depends on a person's own upbringings and opinion.
Personally I don't see video games as a means or a ways to promote violence. There are many things that show violence: movies, t.v., influences, hell even books can be violent. I see it as a way to vent anger, had a bad day? Go blow something up online, or go on a mass murder spree and drive away for 20 minutes in a beat-up vehicle, and come out a much more calm person. There are some cases when video games can affect them (the child, I assume anyone who is old enough to buy mature games is pretty mentally stable to play a violent game lol) too much, and could be a negative influence, and that's where a parent comes in. As long as they have a positive influence on not only what games the child gets, but how they raise the child, violent video games shouldn't be a problem.
But I do fear they can promote violence to those who take them to far and to think of it more then just an escape from reality.
Tough question lol.