I think any media is going to affect how you react to things. If you're constantly watching and playing what amounts to violence porn (Violence itself is the whole point of watching playing -- story is a distant second), then you'll think that violence is more likely to solve a problem than someone who plays Katamari or Final Fantasy, where just causing heads to explode isn't the point.

I'll put it to you this way: Schindler's List and Showgirls both have a lot of nudity. However the purpose is completely different. Schindler's list is a drama about a historical event, and so the nudity is incidental to telling the story. It's not porn, and the whole point isn't to sell sex, make sex look fun etc. Showgirls is much more about tittlating the viewer into thinking sex thoughts about the naked people. In short, the reason the average person watches is to see naked people and think sexy thoughts.