... And we had a long campaign during the 2nd edition Dark Sun years and they were pretty damn evil, many times to eachother.
Maybe I have more of a misconception of evil campaigns than anything. The rare times I've had evil characters in my games, the other players didn't like it and that character's actions had to be changed; however perhaps if everyone embraces the concept at the outset, maybe it simply works better.
It's definitely one of those things that can go south pretty quickly if the entire group isn't onboard, or you have a Player who's simply using the chaotic/evil alignment to excuse dickery. It takes a more mature player to pull off evil or chaotic well, someone willing to realize that such individuals have motivations, rationales for what they are doing, might not even see themselves as "evil", and even if dedicated to the service of a greater evil, will still work with others of a similar bent without necessarily screwing them over needlessly. If you get a numpty who thinks Chaos/Evil is simply random, crazy, and short-sightedly selfish and/or violent, it doesn't tend to go well, especially if the party is mixed alignment. Like everything else, it comes down to "Know your Players" and ensuring that folks are cool with things beforehand or not.