Speaking as someone who, through military deployments, has been aparty to and responsible for Jim's quote en quote "real violence," I have a comment I've held for awhile now about desensitization to violence from media in general. I does and it doesn't. It doesn't prepare or desensitize you to what you see when it's right there in front of you. In the same regard to a flight sim trainer for pilots. I doesn't, and isn't trying, to make the action of ACTUALLY flying the plane indistinguishable from the flight sim, but it makes the fear, apprehension, and hesitation from getting into a real cockpit less fearful. Violence in media is the same thing. I don't care how many SAW's you've seen or other gore flicks, when you see a real head blown off someone, it gets to you. But what seeing those movies or playing games like them DOES do is make you far less likely to recoil BEFORE you see it.
Granted it's anecdotal but I have to go on my own experience, I saw this in action in my own unit. I had a guy that was from the classic, SUPER classic "Brady bunch" family who didnt watch TV growing up, never had video games, didnt read or see violent things. Sheltered in all regards. Then you had me, growing up playing anything and everything, watching everything and anything, doing anything and everything, and "desensitized" to violence in a manner of speaking. When we both, on our first deployment, came across our fist bodies torn by bullets, we both recoiled at the sight. The difference was I didn't hesitate to walk over to look, it took coaxing to get him to come over. I was, more or less, just as bothered by it (but not as long as he was which I'm sure is another factor) but I more readily approached it. That's something I am sure that violent media does do. It takes the COMPLETELY unknown, and gives a person a toehold. Is that inherently a bad thing? No, I don't suppose it is, but does take SOME mystery away from the air of true violence and by definition that would desensitize the fear away from it (fear stemming from the unknown).