So here's the question, is playing a game where you pretend to do horrible things to Eric's Grandma harmful?
There's a school of thought that says you should surround yourself with positive things. Happy people, etc, and stay away from negative things (criminals, abusive people, drugs, etc.).
FATAL seems to be a game about playing out deplorable acts. I suspect players could get into a one-upmanship of depravity. Basically spending more time thinking of horrible things to do.
How is this good for you?
Is it bad for you? Maybe not a in a scientifically proven way, but as a gut feeling of "yeah, it can't be healthy to spend 4 hours of game time thinking about the worst way to sexually assault Eric's Grandma."
There's a sizeable amount of psychological research (at least on the topic of aggression, and to a lesser extent, pornography) that the "catharsis" approach -- i.e.: "getting it out of your system" -- doesn't actually get it out of your system, but rather desensitises you to it. This suggests, for example, that "punching a pillow when you're angry" actually teaches you that punching is an acceptable behaviour when you're angry, as long as the target is a pillow; "punching a pillow" therefore doesn't make you at all less violent when angry, and in fact, might gradually teach you to become
more violent.*
So as far as playing FATAL goes, according to this theory, playing FATAL definitely
won't "get the (depravity) out of your system". Over time, FATAL might actually normalise depraved behaviour in your mind.*
*The key difference between catharsis "not getting it out of your system" vs. catharsis "actually making things worse" is normalisation. If you punch a pillow only once, or pretend to commit some depravity for a game only once, you probably won't start to (subconsciously) feel this behaviour is normal, and therefore aren't likely to apply it other circumstances. On the other hand, if you punch a pillow every time you get angry, or pretend to be a pedophiliac rapist every Wednesday evening, eventually you will start to (subconsciously) feel that this behaviour is normal, and gradually you might become more likely to apply that behaviour in other circumstances. In short, if trying to "get it out of your system" becomes a habit, your effort is probably making things worse.
(This is why social workers, for example, can deal with abusive or drug addicted people all day without becoming abusive or addicted to drugs: the social worker probably never starts to think that being abusive or using drugs is "normal" or appropriate behaviour.)
I doubt that the scientific debate on this is settled, but this is the dominant belief on this matter in the psychological community these days, as I understand it.