The human brain needs to relive the worst events it's experienced in order to properly heal itself. Psychologists used to do it by having PTSD sufferers talk through the experiences over and over, but simulating the events takes the process one step further. The games have been proven to help release the stored anxiety as they, in essence, desensitize the soldier to the severity of the memories.
A recent study of Vietnam veterans found a 45 percent reduction in self-reported symptoms with the games. It also works for other people who have survived non-war related traumatic events -- for example, simulated driving games appear to help car accident victims get over the phobia of motor vehicles that sometimes results. Really, it should work for anything where exposure is needed to help a person get over their fears -- one clinical psychologist is using it to treat everything from a fear of flying to a fear of spiders. Damn, when the future arrives and space marine becomes a real job, this whole generation is going to be trauma-proof.
"An eternity of slaughter and the laughter of thirsting gods? Count us in."