To start off, I think Wayne LaPierre's news conference blaming the culture was all wrong. Furthermore, the NRA itself is responsible for much of the "jackbooted thugs" culture that directly lead to the atrocity in CT.
But to what extent do video games encourage violence? Adam Lanza spent hours playing Call of Duty and you can't completely discount this from his psyche.
Personally, for me, shooter games just end up numbing me, but that's also because I"m not really into guns and so like rifles and submachine guns feel the same. I'm sure that for guys really into guns, the distinctions between teh different firearms are like the draw of the game.