So you don't think that tackling the problem of bad parenting is more important than the problem of buying violent videogames ? I personally think that educating and somehow (I don't know how, it's not an easy answer) making parents in North America better and more accountable for how they raise their children is more important.
And where does it end ? If a child kills because his warped mind couldn't comprehend what he read in the bible do we get the government to ban that too ? What about drugs ? If record numbers of kids start doing cocaine at 12 years old then who do we blame ? Well, we didn't blame the parents when the kids turned into killers so why blame the parents when they turn into drug addicts ?
The situation is somewhat like the war on drugs. The American government spends billions of dollars on stopping the traffic of drugs into the country (which is basically impossible) instead of focusing on what makes people over here want to do drugs in the first place. It is far easier for the government to deal with the supply rather than asking why there is a demand.