1) Each and every bit of children their parents should be responsible for.
Children are not yet ready for the world. So parents are the most important ones who should show them path.

2) Video games come with maturity levels printed on it's case. Sometimes parents don't even bother to check that.

3) No video game can be solely responsible for some sort of mental illness(Which includes unsocializing, violent acts, hopeless behaviors).
There must be improper guidance of a unprepared mind or ignorance or expose to abuse or there are endless ors.
Just because violence is exposed to us we don't become violent, because we have become matured through proper way of guidance and we do own such resistance for such stuff.
Proper education and culture has already been injected in our veins so that we can decide amongst good or bad.
Who holds the responsibility of doing so when we are immature(when a child), obviously the parents.

4) Recent(Not much recent though) researches have shown that video games increase mind flexibility, physical analytical skills and ready wit.
For those who are blaming games, there are adult(Mentally) novels, but we don't give them to children because they are not ready for it.
We give them only those books which are suitable. I guess you can relate what I'm trying to state.

5) I'm quoting someone others comment here:
"I doubt that majority of people who are involved in violent crime have a lifestyle background of sitting on a PC playing games. They're far more likely to be outside hanging around in gangs."
- Luhng - 2/26/13 8:09 PM

6) Those parents who cannot give proper guidance and time to their children thus making their children exposed to improper things (which include Video games) are actually still the unprepared minds who are incapable of controlling their children and blame it on others.