Madness? Nope, don't use it. I've never had a PC, who had been tortured and brutalized by one of the NPC's develop a hysterical fear of restraints and fire pokers. Never had an insane wizard blasting spells at things that only exist in his fevered imagination. Never, ever, ever had some poor slob who was driven mad, and now the party would have to take care of them while they tried to accomplish the mission, important clues appearing in the babbling of this madman.
OK, so I have. I've used everything I could. The Wizard who heard voices telling him to kill everyone. The PC who was terrified of the dark.
Rape: Hmmm, Nope, I'd never used that in my Ravenloft game. Nobody ever gets drug into an alley and brutally raped and murdered. Oh, wait, yes they do. All the time. My regular D&D Games have it also. It rarely happens to the PC's, but sometimes it does. Some crazy bastard jumps a female PC (The same freak that the PC's are hunting for his string of serial rape/murders) when she goes off alone. He tries to subdue her and tear away her clothing so he can get down to business. It's a literary tool, nothing more, in my game. We don't have descriptions of the actual goings on. I'm running a D&D game, not an interactive porno.
Slavery: Exists in my campaigns, as does serfdom, bondsmen, indentured servitude, the whole works. Some are not that harsh (The serfs of Artik-Huln for example: They will collapse from exhaustion after carrying a hoe across the yard. The serfs are lazy and shrewd, the nobles are soft hearted and have no conception of what actual work is like) while others are brutal and cruel.
War-Hmmmm, that's a tough one. The Lich King War. The Ascension War. The War of Mastery. The Clan Rift War, The Human/Vampire War, The Second Lich King War, 14 Humaniod Wars.
Nope. We don't have wars in my campaign.
Since we are on the topic of evil, what about genocide? I remember it appears in Dark Sun, but let's face it, since orcs are an intelligent life, how do you rational the apparent attempted genocide whenever the orcish armies are put down? Face it, PC's kill men, women and children when dealing with them. What if you inserted a race of creatures that were "almost" kobold, but slightly different enough to warrant thier own genus and god. When the last of them is killed, the god begins wailing about all of his children being slain, and that the PC's have slain the last.
Concentration/Prisoner Camps: How do you deal with those, or do they come up. We've had the in my game. At one point, the PC's snuck behind enemy lines during the Humaniod War and released a camp full of prisoners that were used for rape, slave labor, sport and experimentation.
Terrorism: While it may sound like something that belongs in modern or sci-fi games, it doesn't. My party has been after a bastard who throws fireballs into churches and schools, casts blade barrier into guard houses, ect ect ect. The guy is dangerous, soaked in blood, and the characters caused him. Makes for a bit of personal stake.
On other, "evil" things.....
One of the evil warlords not only wants to exterminate gnomes, because he thinks that thier noses are too big, he's also a child molester, a slaver, a coward, and a mad man to boot.
The players hate this guy too.
The fact that he is a child molester is not very well liked, but let's face it, there have always been those freaks out there. We're not talking 13-18 year old kids, we're talking 5-9 year old girls and boys.
Human Sacrifice. What if the PC's could not interfere? Human sacrifice like the ritualized, institutionalized rites of the Aztecs and the killing of criminals in ancient Wales would both be acceptable in ancient times.
What if someone the PC's like drew the bad lot (IE: The Lottery) and was going to be sacrificed on the Solstice. Imagine the players confusion when thier friend, a decorated veteran, minor noble, and all around square-peg guy, begins wandering around with a dreamy, euphoric look on his face? No mind control, he just realizes that he gets to give the ultimate service to his god. (Inside the most normal appearing people is a crazed zealot) Should the PC's stop it? What if the party finds out that thier friend had to ENTER the lottery in order to be chosen, and can back out at any time? Is it right for the party to interfere? Should they?
Of course, you can mix several of these. A crazed serial rapist/killer who preys on young children, and after raping them, sacrifices them to a dark god that exists only in his mind should have every PC practically fist fighting to be the ones to introduce the freak to Mr. Blunt Object. Make it so that he preys on slave children, so nobody cares but the slaves.
I say, go for all of the above, if your game and your players can handle it. If not, hey, nothing wrong with that. Opening that kettle of fish can be difficult, and you never know how some people may react.
I'm very careful nowdays, since the one day I described to the party what was going as they were running at the dark knight, and he was tearing the maiden's clothing off and bending her backwards over a rock with his knife in his hand (That's about as detailed as I get nowdays, right there) and questions got asked, so I added a little more detail.
Then I happened to catch the eye of our devoutly religious (no, I won't say what religion, he is not a general representation) player, and almost stopped in mid description.
The drool at the corner of his mouth, and the gleam in his eyes said volumes.
So now, I'm very careful who is there at the table when these topics are discussed, and very Victorian in my descriptions.
Some times, the nicest wrappings conceal the most disgusting objects.