Disgust is good. Disgust works.
This New Science article discusses the science of disgust. It doesn't much address the potential for socially-determined disgust to be harmful, though.
Lance Workman, a psychologist at Cardiff University says, "In some parts of the world people eat tarantulas, which is something that would disgust most people." The article says Workman believes such people have learned to suppress their disgust.
Interesting how he supposes that we should have a predisposition towards disgust for tarantulas. What if it's socially acquired? Learned? The article does point out that some people have an irrational disgust for cancer patients, despite the fact that the condition isn't contagious, but it doesn't really discuss the harm that sort of disgust could engender: alienation, deprivation of much-needed touch, affection and compassion.
My concern lies in that I could see some folks justifying their hate, bigotry, homophobia, etcetera, by asserting that it's "natural" disgust for the unclean or the "unnatural," as so many gaybashers like to say. (Interestingly enough, the survey which this study was based on didn't include disgust of a sexual bent.) Just because something is "unnatural" doesn't make it wrong or worthy of our contempt. Or disgust.
In fact, I'd argue that determing what's "natural" versus "unnatural" is an often difficult and sometimes futile enterprise. The idea tha "natural" is somehow automatically better than "unnatural" is certainly fallacious. It's quite "natural" for some creatures to eat their spouses or to kill their young. It might be quite "natural" for a virus to extinguish all of humanity within a matter of weeks. I'm sure we'd all agree, however, that it'd be mighty nice for a scientist to come up with a counteragent, however "unnatural" which would deliver humanity from the brink of extinction.
Another example: It's arguably "unnatural" for us to live into a tenth decade. What's probably "natural" is for us to succumb to some sort of virus or disease in our mid-40s. But few people seems to decry the idea that we should pursue longer lives through science, medication, surgery, cryogenics, whatever--even in pursuit of immortality. Arguably, we're motivated by disgust to pursue immortality, too--by our disgust with death. So, in this case, we're motivated by digust to do something "unnatural."
In other words, we're pretty selective with our disgust. Guess that's because death is something that affects us all.