From talking to some of my friends in the 'Smart Redneck' category, it occurs that their gut contains more information about a lot of the things that make most neurotypicals say 'ick' than just 'ick'.
For instance, the usual response by a neurotypical to the idea that people could sell, rather than just donate, organs (usually kidneys), comes out as 'ick'. Sometimes Second Sigma Sophists wrap it in a veneer about 'exploitation' or 'social justice', but they don't actually believe that, at least by the revealed preferences test.
However, talking with some of my allies in a pure listening mode, lubricated by a few drinks, one finds that their guts contain more than ick or folk Marxist sophistry.
One concern is that if kidneys, et al, are saleable, that the value of same will be entered onto every person's 'balance sheet', and taken into consideration before eligibility for things like financial aid at college, Medicare/Medicaid, and the like. They agreed with my basic argument that people are selling chunks of expected lifespan all the time with jobs like roughneck on offshore rigs or contractor in dangerous areas. It probably helps that some of them have actually worked such jobs themselves. My suspicion is that they grok that the delta from forbidden to mandatory is awfully small in 21st century America.
A related concern as regards legalization of prostitution would be that women would be EXPECTED to accept jobs in that 'growth industry' should they be unemployed. I vaguely recall a case to this effect from Germany some time back, so frankly that concern is hardly paranoid. It's just one or two unprincipled exceptions away.
The common theme in all of these things is that it is really hard in the US for something to be legal but discouraged and low status, especially when the Cathedral lawyers get involved.