Fellow video game players, let's admit one thing: playing violent video games does desensitize us...
...to the violence in video games.
In violent video games, I have shot pistols, rocket launchers, missiles, and grenade launchers. I have killed computer characters, I have killed other players. I have battled monsters, slain dragons, and shot lightning from my fingertips. I have died and I have been killed, over and over again. To all this, I am desensitized - within the game.
In the real world, I couldn't even find the safety on a handgun, I can't imagine ever shooting anyone, the monsters stay under the bed for the most part, I'd shit myself if I ever saw a dragon, and I'm never going to become Emperor Palpatine. Beyond that, I'm just as terrified of death as everyone else is.
Look, what was more relevant to what happened at Sandy Hook:
(1) The gunman playing Call of Duty?
(2) Or the gunman going to shooting ranges with his mother and actually shooting a real weapon at real targets?
What desensitizes us to committing acts of violence in the real world is seeing violence in the real world (and often being the victim of it as a child) and subsequently doing violence in the real world. Sure, they train the military with video games, but that's to learn how and where to move. Learning how to kill? How to deal with the emotion that produces? That can't be taught in a video game, nor can it be learned from one.
Let's focus on the most directly-related issues to real-world gun violence: mental illness and the guns themselves.
(By the way, here's wikipedia for the summary of actual research on this topic).