Of course the dividing line between mercenary, soulless capitalists and defenders of human dignity is not always clear. As Mr. Roth pointed out, ideas about what is repugnant change all the time. Selling oneself into indentured servitude was once thought permissible, while charging interest on loans was not.

In recent years groups have fought over whether it is acceptable to display and sell art that offends religious sensibilities, like a photograph of a crucifix in urine or a sculpture of Jesus on the cross, made out of chocolate. “Bodies ... The Exhibition” and similar shows, which feature the preserved and dissected remains of people, would once have been considered both ghoulish and profane. Although religious leaders, human-rights activists and medical officials have condemned the cadaver exhibitions, the displays have attracted millions of visitors in the United States and around the world.

And last week a woman in Ohio whose ad to sell a horse mistakenly appeared under the heading “Good Things to Eat” in a newspaper’s classified section received dozens of calls, some expressing outrage and others from people interested in turning it into dinner. (In Europe and Japan horse meat on a menu would stir no more comment than macaroni and cheese would in an American diner.)

Arthur C. Brooks, a professor of government and business at Syracuse University who moderated the Washington panel, spoke of how he  like thousands of other Americans  carried $7,000 in hundred dollar bills to ease the adoption of an abandoned baby in China despite a visceral reaction against the idea of buying and selling children.

“It’s very hard to predict what’s repugnant and what’s not,” Mr. Roth said. Paul Bloom, a professor of psychology at Yale, agreed. He conducted a two-year study to try to get at why people consider athletes who take steroids to be cheating, but not those who take vitamins or use personal trainers. He and his team offered different possibilities: What if steroids were completely natural? Or were not at all harmful? Or were only effective if the athlete had to work harder than before?