http://www.truthout.org/joe-brewer-why-you-should-care-about-psychology-disgust59979One of the major discoveries so far is that morality is grounded in our bodily experience. We literally feel right and wrong in our bodies. Disgust is a physical experience that applies to notions of moral purity, moral health, and our judgments about how to handle situations like incest, cannibalism, and rape. For each of these emotionally potent topics, the strength of our feelings corresponds directly with our sentiments about how they should be handled in society.
Research tailored to the study of moral purity and the emotion of disgust was conducted by Paul Rozin, Jonathan Haidt, and Rick McCauley. (A copy of their seminal article can be requested here.) They showed that the physical experience of disgust provides the bodily foundation for the moral concept of purity. Put succinctly, when you experience the feeling of moral disgust – via the tainting of something you hold sacred and pure – it is produced by the same neural and chemical process that arise after biting into a moldy piece of bread or some rotten fruit.
The experience of disgust is very persistent. Once we associate those negative feelings with an idea (like 'liberalism' or 'Obama the Muslim') it is very hard to shake off. The explanation for this comes from the field of evolutionary psychology, which explores the evolutionary origins of human thought and behavior. Animals that remember the foods that make them sick are more likely to survive and reproduce. So those who have a long memory of disgust are better adapted for survival.
Applied to politics, this phenomenon implies that once a political idea becomes a rotten apple it will remain a rotten apple. Disgust tends to stick around. This is why so much time, effort, and money is dedicated to painting the opposition with negative feelings. If a disgust response can be evoked, it will tend to stay around.
Think about the ramifications for gay marriage. If children are taught that homosexuality is disgusting, they will want to stay far away from it. As their moral sentiments develop, they will begin to see homosexuality as a contaminant in society. When thinking about the sacred institution of marriage, they will feel the threat of this impurity to something they want to keep clean. It's pretty easy to mobilize them against this threat because the feeling is long-lasting and easy to activate with a political sound bite.
There are two lessons to learn from this. First, if you want someone to support your idea (like the notion that addressing global warming might be a sensible thing to do), don't let it get associated with disgust (such as how people feel about the elitism of scientists - be it real or imagined). Second, if you want someone to oppose an idea, just riddle it with associations to the profane and impure. Do so with references to basic bodily functions and you'll be particularly effective.
These tactics have long been used in politics to the detriment of civil society.