Harvard Economics professor Alvin Roth has a thought-provoking paper titled “Repugnance as a Constraint on Markets” (that’s an SSRN download; PDF file here).
He begins with a look at California’s horse meat laws, which forbid the sale of horse meat as human food despite the lack of any legitimate public health concern, and there’s extended discussion of laws forbidding human kidney sales. Nothing logical about that; it’s just that some people find eating horses repugnant.
As someone who finds the eating of dogs repugnant, I can understand. But I admit there’s nothing especially logical about it. I see dogs as “man’s best friend” and as having voluntarily domesticated themselves in a manner unlike animals raised for meat, and thus I see eating them as a betrayal of sorts. Again, this is a feeling thing, and not especially logical.
To give repugnance historical perspective, Professor Roth has compiled a table of “Markets In Which Some Transactions Are, or Were Once, Repugnant“:

Human remains
Cadavers for anatomical study, organ donation,
bone and tissue
Live donor organs (kidneys, livers)
Indentured servitude, slavery
Volunteer army, mercenary soldiers
Discrimination based on race, gender,
handicap, marital status, etc.
Reproduction and sex
Surrogate mothers, egg and sperm donation,
abortion, birth control
Prostitution, pornography
Brideprice, dowry
Polygamy, gay marriage, incest
Words, ideas, and art
Obscenity, profanity, and blasphemy
Cultural treasures, art, and antiquities
Life insurance for adults, children, and
Prediction markets
Short selling, currency speculation
Interest on loans
Pollution markets
Tradable emissions entitlements
Dirty industries in less developed countries
“Price gouging”
After natural disasters
Ticket scalping
Sale of indulgences and ecclesiastical
offices (“simony”)
Endorsements/payments for amateur
versus pro athletes
Drugs and sports
Food, drink, and drugs
Horse and dog meat
Alcohol (Prohibition)
Marijuana and narcotics
Vote selling and bribery

It’s fascinating to see a list displaying all the things which have been regulated because of feelings of repugnance, and bear in mind that as an economist, Roth’s concerns are with market-related activities. (Needless to say, a myriad of repugnance-based laws exist — so many that it would be impossible to list them.)
What really drove home for me the emotional nature of repugnance was the realization (in the kidney market discussion) that repugnance overrides the preservation of human life itself. Apparently, it is considered better for kidney seekers to die than for them to pay donors for their kidneys, because the latter is seen as “exploitation” — which (assuming there is such a thing) is apparently more repugnant than people dying who could be saved:

All parties agree it is urgently desirable to cure patients with end stage renal disease, and that the best current treatment is organ transplantation, particularly from live donors, and otherwise from deceased donors. The current situation in the United States involves long wait times for deceased donor kidneys by tens of thousands of patients without a live donor, difficult and costly palliative treatment by dialysis, and thousands of deaths annually while waiting. But opponents of organ sales find the prospect of a market for organs so repugnant as to be apparently worse than the current situation. Proponents of markets are correspondingly frustrated at the failure to adopt what they see as a feasible solution that could be implemented quickly.

Better thousands die than one person be “exploited.” If there is such a wisdom as the “wisdom of repugance,” I think this carries the concept too far.
But I want to be fair to the other side, so I should start by asking a basic question.
What is exploitation?
Obviously, starving fathers in impoverished third world countries, mental defectives who do not know what they are doing, drug addicts who need money, or chronic gamblers in debt to the Mob — such people might be expected to sell their kidneys at bargain basement prices. Market forces being what they are, it would not be unreasonable to assume that with thousands of kidney buyers worldwide, if the market were completely unregulated some of these people would be willing to be taken advantage of, and prices would fall accordingly.
But at the other extreme, what if a very wealthy man needs a kidney, and he’s willing to pay anything for it? I don’t especially want to donate one of my kidneys to a total stranger for a number of reasons — not the least of which is life is riskier with one kidney. You rupture your one kidney in a car wreck, and then you become one of the thousands of prohibited buyers waiting in line. If the recipient were a friend, I’d be altruistic enough to consider it. (In that respect I admire Virginia Postrel for donating hers; it’s not an easy thing to do).
But suppose the wealthy man offered me a million dollars. That’s just a figure off the top of my head, but I’d want some assurance that I’d have money in reserve to cover the possibility of having to get another kidney, if the good one went kaput.
I might just take the million. It would be hard to make the case that I was being “exploited.” Suppose further that the rich man tracked me down because he had information that I was a uniquely compatible match with his immune system, and that there was no way a kidney from me would be rejected. It could be argued that I had the advantage over him, and that in fact he was the one being exploited. I mean, I’d arguably have the power of life and death over him, which means I could squeeze him to pay far more than the normal market rate. Can millionaires be exploited too? Or is this something that can only be done to the poor?
I suppose it could be argued that I have just demonstrated the immorality of not just the kidney market, but of market economics generally, for if we examine any transaction, we might be able to find evidence of duress on one side or the other. But does this make the transactions immoral? Why? Most people want to live longer lives and will pay whatever they can afford to increase their odds. Many will pay huge amounts of money in their quest for happiness, and this could mean anything from drugs to sex to gambling thrills to power to fame to the latest BMW. How much someone is willing to pay depends on the level of the individual’s interest, or obsession.
The fact that we do not all share the same desires and tastes complicates any analysis. I have no interest in gambling, so I find it hard to identify with the idea that a guy who mortgages his house for one final night at the high roller table is being exploited. I consider him merely a fool. Ditto people buying new cars they can’t afford; I’ve never bought a new car in my life and I find it hard to sympathize with people who go into unaffordable debt that way. Or with poor people who bankrupt themselves on consumer items I can do without. Or people who eat junk food no one makes them eat. (Seriously, I had a huge argument once with someone who told me McDonalds exploits the poor. If I had to live on a pittance, I’d buy beans and rice. Why was I told I was “cruel and insensitive” for not sympathizing with people who won’t economize?)
Anyway, repugnance is at the core of the definition of “exploitation.” But some people are more repulsed than others, and by different things. I tend to see people dying because they’re not allowed to buy kidneys as more repulsive than the idea of someone selling a kidney under duress. I also see a socialist super nanny state as more repugnant than the spectacle of poor people throwing their money away on junk food and things they don’t need.
Like it or not, what we have seems to be a system of competing repugnancies. Libertarians like me can yell all we want about the moral virtue of an unregulated market, but the fact is that the market is going to be regulated, and a major reason is that people find certain things repugnant. That’s why we had Prohibition of alcohol, why we are approaching a new prohibition with tobacco, and why we are rapidly approaching an American state which can be called genuinely socialist.
I think there’s a principle of the squeaky wheel at work. Whoever yells the loudest wins. With dueling repugnancies, the squeaking wheels involve competing moral claims. Thus, people whose moral claim is that homosexuality is repugnant are locked in a struggle against people who claim that not only don’t they find homosexuality repugnant, but they find “bigotry” morally repugnant.
But kidney sales are not a culture war issue. Compromise might take the form of lessening the regulations to allow sales according to a system of guidelines to prevent the sales of kidneys by people under duress. These could be court-supervised or professionally-mediated, but no system would be perfect. I mean, just as I feel sorry for impoverished Third World peasants, I feel sorry for the rich guy willing to pay anything for the compatible donor, and I also feel sorry for the guy who’s going to have all the teeth knocked out of his mouth, his legs broken, or worse, because he can’t pay a gambling debt. In the latter case, the kidney sale might save two lives, but it would still be exploitation. Which begs the question of why it is wrong for the Third World peasant to permanently advance his family’s situation by selling a kidney. It’s not clear to me where the greater immorality lies, or why.
I often like to imagine a world ruled by logic and not emotion, a world in which laws would not be passed because of “repugnance.” Yet I can’t really say that I am always repulsed by repugnance, for there are many things I find repugnant.
The most that can be hoped for is that people admit to and acknowledge their feelings of repugnance, for at least that way discussions and arguments can proceed in a more or less honest manner. It is when people confuse their feelings of repugnance as facts, as logical objections, or as independent objective truths, that problems develop.
I’m a bit too tall to be a dwarf, but I’m a fairly athletic person, and were I a foot or two shorter, who’s to say that I shouldn’t enjoy being tossed around for money? Obviously, those who think it’s disgusting, that’s who. The political process gives them the power to do that, and if the dwarves don’t like it, they can band together and fight it. I might wish they opponents of dwarf-tossing would spare me the claim that their objections were grounded in eternal truths, because that only makes me want to counter them with alternative truths, and the truth process is distorted.
I think that what gets called “truth” is often based on what people like, and what they dislike. But to many people that thought is itself repugnant.
They should bear in mind that this is only my repugnant opinion. I refuse to lay claim to any repugnant truths.