I think video games do desensitize the youth from images of violence. A child that grows up playing graphic, photo realistic, video games that depict violence to a certain degree of accuracy are bound to become more accustomed to even real pictures of violence (depending on the severity, of course). I do not believe blankets often fit too many people, so there are always exceptions. I do not think that such people are bound to be desensitized to violence in real life. Seeing blood on a screen is different than seeing blood on your shirt, shoes, or hands. Aversion to blood and violence aside, I think the average person would fear repercussion from the law to a degree great enough to dissuade them from partaking in any particularly violent acts. I'm sure most people don't have a problem with pounding someone's face in. Most people fight someone in their life, regardless of whether they are the aggressor or defender. However, giving someone a bloody nose or a split lip is far different than plunging a knife in their gut or placing a bullet in their head. I think the divide is lethal and non lethal violence.
From my own personal experience, I've seen all sorts of violence on television. I'm not talking in shows, but film and images from previous wars. Dead soldiers heaped up in piles, the charred remnants of holocaust victims, ect. However, I can honestly say those images never bothered me in a graphic sense. I felt more for the horrendous waste of life, than I felt queasy at the imagery. Would I have felt differently without video games? Maybe, I don't know. I used to think that no matter of violence would ever bother me. That I can see any sort of harm befall the human form and not flinch. That changed a few months back, upon stumbling upon a video of the Mexican cartel. They slit open the throat of a rival cartel member. They slid the blade across his neck, and then pulled his head back by his nose as if he were some mass of meat to be butchered. It disturbed me. I couldn't finish the entire video. The sounds he made, the way his body trembled and flinched, I couldn't finish it through. I've seen pictures of street shootings. I've seen images of brain on the sidewalk, and images of people bleeding from stab wounds. I've seen all of that, but I've never seen the process so up close and personal before. It seemed more real. I saw a man die, albeit on a screen, and I have no desire to see something like it again.
What this means is that while I may not be everyone, I think video games only desensitize to a point. Video games are a cold, unfeeling, unreal depiction of whatever is on the screen. They are pixels, and you know they are pixels. When that mass of pixels explodes into a red, gory mess, it isn't personal. You know it's a game. I think any sane, healthy minded person will have a natural aversion to extreme violence that is real. However, video games, just like anything else, can certainly influence the psyche of any person, but an unhinged person was bound to be unhinged regardless.
Caligula certainly did not have any video games.