Basically, Haidt makes a connection between general cultural attitudes -- liberal, conservative and libertarian -- with one's level of disgust. The mouth was the first and most important portal, and we developed a disgust to things that would make us ill. Extrapolating this concept he sees different levels of disgust toward cultural issues, gay marriage, for example. So the hypothesis is that conservatives have more sensitivity to things that disgust them whereas libertarians have the least.
But that's too simplistic for such a complex idea. Go watch the 35 minute video and see for yourself.
His audience was mostly libertarian, and while they gave him positive feedback, he did challenge them with some interesting hypothetical situations. After describing the situation, he asked the audience whether they were (A) totally OK with it, (B) morally ambivalent, or (C) thought it was morally wrong. Here were the scenarios:
First: Birth control that prevents conception.
Second: Chemical abortion one week after conception.
Third: Abortion at six months after conception assuming the fetus feels no pain.
Fourth: A rich man would like to have sex with young girls, but he would never want to cause any harm. So he purchases human eggs and has a lab fertilize them with his own sperm for a female fetus. He pays a woman to be the surrogate mother. At five months gestation he pays a surgeon to sever the fetus' brain stem so that it will never have any cognition. The result would be a living female body with no feeling or awareness. Then at around age 13 he begins having sex with it.
I think he found a way to gross out libertarians.