Easy rebute to that sort of nonsense.
Video games didn't exist even 50 years ago. Humans have been extremely violent by nature for as far back as we can go.
Therefore, Video games cannot possibly be responsible for something that happened beforehand. Its like blaming someone for a murder before they are even born - its utterly stupid.
If anything, Video games seem to make people less violent as they get their anger and frustration out during gameplay.
The only thing that can be said in regards to violence and video games is that they are violent because we as humans enjoy violence.