Disgust is powerful, and powerfully negative. And I agree with Leon Kass that we should listen to our emotions when we analyze our moral vocabulary. My sense is, however, that even the most apparently unconditioned, natural, visceral reactions are shaped in part by cultural (and moral) expectations. In other words, it's not a one-way street from biology/nature/evolutionary adaption to culture and morality. We feel disgusted at least in part because of prohibitions and proscriptions.
Recall that I came to this debate because of the social-scentific claim that conservatives have a stronger sense of disgust than liberals (see for example: http://www.wired.co.uk/news/archive/2012-08/24/disgust-breeding-conserva...). I am still deeply skeptical about this claim. But *even if* a correlation can be found between measurable reactions to disgusting stimuli on the one hand, and political ideologies on the other, what do we really have?
A simple answer is this: conservatives are "easily disgusted" not because of biological hardwiring but because of ideological influence. Perhaps it's simply the case that conservatives are less likely to trust the cultural and social encouragement to overcome what might be an initial negative reaction. This issue of trust goes back to what I mentioned about cuisine in an earlier post: most of us aren't born with adventuresome palates. An expansive sense of taste has to be taught, and this involves a deeper commitment of trust in two senses. One has to trust the teacher, and one has to trust the world. The risk has to have its reward. This is perhaps the "moral" point about an expansive and adventuresome palate: in overcoming an initial aversion to strange tastes (bitter, sour, umami) one gains comfort and even confidence about some of the rare joys that the world offers.
Cultivating confidence in this sense means overcoming disgust. I would suggest that this illuminates at least something about the split between conservatives and liberals.