Well it is true that while you yourself might consciously know the difference between what is fake (simulated) and what is real, the brain's ability on a sub-consicous level cannot. Therefore a person who has seen too much violence or disturbing images within their sensorium is indeed fucked in the head, and one can be prone to be "Not Disturbed" by what should disturb one. Also if the mind thinks that something is real, (i.e. a scary movie freaks you out suddenly) the body produces adrenaline and other endorphins no different than if you were in a life or death situation. Too much can seriously alter a person's health.
That said however... aside from the permanent damage to one's health due to excessive amounts of adrenaline (and others), assuming it's a regular habbit... a person is fine as long as they can understand where lines are drawn. I'm the dude who laughs @ the movies when someone gets blown up, or shot in the head and it's filmed from an odd angle or something. Most ppl don't laugh and think it's weird... but then a part of a movie that's supposed to make me laugh is "Stupid" to me and I might at best smirk. This pychosis is probably brought about from having seen too many violent depections and getting myself into some very REAL "real life" situations where the final solution was violence. I think this is what a lot of ppl against video games are trying to get at a lot of the time, but until the day we can all be arrested for thinking, well then it shouldn't be anyone's business to tell others that something is too violent, or too risque for someone. I enjoyed the heck out of Man Hunt when it first came out, but I didn't go and start committing mass murders either. Thus that study on violence in games is just another compiler piece for the masses to use against others, that will ultimately get picked up by a moronic politician at some point and then with little to no understanding of the actual gaming hobby or industry try to "Cleanse" things.
Interesting, but utterly worthless as most of those studies end up.
MERCENARY X99