How do you maintain an audience's interest with a deliberately unlikable main character?

Hm....to really make an unlikable character workable, the answer has to at least include confidence. He has to believe in what he's doing. For some reason people can be pretty merciless when it comes to the weak, and characters who do dark or selfish things without believing in their actions will get a double dosage of hate. It also helps if your MC is clever and smart. Think like House.