As for corruption, World of Darkness does that rather centrally.
Basically if you do a bad thing (even if you're forced or coerced) you have to roll a degeneration check. If you *fail* the check, you rationalize what you did, and your moral character erodes. If you pass the check you feel true regret and maintain your values. Like most WoD rolls it's expected for the storyteller to add modifiers based on how the player RPs the situation. Like, one of our party stole a guy's wallet for no reason and explicitly didn't give a crap: He got a -2 which meant basically no chance to pass (there was a slight chance of his conscience speaking up, I guess).
Thing is, now that he has 6 humanity instead of 7, he never has to roll degeneration for petty theft again. He'd have to do grand theft, like burglary, or something worse like assault. Most vampires stabilize at about 5 humanity apparently, where any amount of theft is okay but arson or manslaughter still worries their remaining conscience.
It's actually related to sanity because, every time a character loses humanity, they have to roll for "derangement". If they can't keep it together, they get a psychological problem from their inner turmoil. Typical example is vampires believing they hear the souls of their victims for several hours after feeding. This can happen from particularly traumatic events too, though, like a character who nearly dies gains a phobia. There's a long list of possible derangements, and it can be random or up to the storyteller.
Edit: So in a nutshell: WoD characters can go crazy from seeing traumatic things. But if they get jaded and amoral, they become resistant. Though vampires with high humanity get interesting benefits, if they can maintain it. Regaining lost humanity costs a lot of experience points.