It seems that violent games may indeed desensitize players—but in a way that can actually be helpful.
Researchers at Keele University in the UK have found that playing a violent video game can give players a higher real-world tolerance for pain. The study had 40 participants playing both a violent first-person shooter and also a non-violent golf game, and found that on average, playing the FPS significantly increased participants' pain tolerance:
Participants played both the violent and non-violent game on separate occasions for 10 minutes and then placed one of their hands in ice-cold water to test their reaction to pain. On average, participants kept their hands in the icy water for 65 per cent longer after playing the violent game, indicating that playing the game increased the participants' pain tolerance. Heart rate was also shown to increase.
Dr. Richard Stephens, who led the study, explained that the impetus for the research had come after previous studies showed that swearing actually helped alleviate perceived pain. They theorized that aggression set off the body's "fight or flight" response, in turn changing how pain is felt and increasing the heart rate. The study using video games "was a test of that assumption in which we set out to try and raise participants' aggression levels by having them play a violent video game. We then tested the effect on pain tolerance. The results confirm our predictions that playing the video game increased both feelings of aggression and pain tolerance."
So, if you're recovering from a painful injury or illness, it might not just be intentional games for change or distracting experiences like Final Fantasy that help. Go ahead and shoot some virtual people and zombies.