There just aren't enough organs to go around. About 75,000 Americans are on the waiting list for kidney transplants. But in the coming year, just 18,000 will get them. That's only one in four.

It's not as though the others will eventually get kidneys if they just wait, sustained in the meantime by dialysis. In the next year, nearly 4,000 of those patients will die waiting. At least 1,200 others will fall off the list because they develop complications that make them too sick to withstand a transplant.

Thousands more transplant candidates might be saved if more Americans signed organ donation cards, if more families consented to donation of their loved ones' organs, and if medical personnel approached the families of potential donors more often. But the supply of cadaveric organs has been disappointingly flat.

So in recent years, there's been a push to persuade living Samaritans — relatives, friends and even strangers — to donate one of their kidneys. That's helped, but not enough.

The situation has sparked recent debate about what was once unthinkable — paying people to donate organs. Six experts recently tackled that emotional issue in an Oxford-style debate, the last of this season's events in the Intelligence Squared U.S. series.

The proposition: "We Should Legalize the Market for Human Organs."

By the end of the session, many of the "undecideds" were persuaded. Before the debate, 29 percent were uncertain. Afterward, that declined to 9 percent.

Those who favored buying and selling organs went from 44 percent to 60 percent. But those opposed inched up only 4 points, from 27 to 31 percent.

The debate took place before a capacity crowd on May 13 at the Asia Society and Museum in New York City. Ira Flatow, host of NPR's Talk of the Nation: Science Friday, moderated.

Organ sales are illegal in the United States and most other countries (Iran is a partial exception). The National Organ Transplantation Act of 1984 states, “it shall be unlawful for any person to knowingly acquire, receive, or otherwise transfer any human organ for valuable consideration for use in human transplantation if the transfer affects interstate commerce.” The penalty for breaking the law is a fine of $50,000 or up to five years in prison, or both.

In Libertarian Land, organ markets are legal. This makes everyone better off.

Consider first kidneys. People have two but can live normally with one. If the kidney market were legal, a person whose kidneys fail could purchase from a willing seller, and both could then live healthy lives.

The seller would risk that their remaining kidney might cease to function, but in a legal market, the supply of kidneys would be large and the price low, so such persons could likely buy a kidney from some future seller.

The situation is similar for liver transplants; recipients need only a partial transplant, and the donor’s remaining liver regenerates.

What about more extreme cases, where someone wants to sell a heart or other vital organ?

Such behavior might sound irrational, but imagine an aging parent in poor health (unrelated to their heart) who could earn a large sum by, in effect, committing suicide and selling their heart. The income might make it possible for that person’s children to attend better schools, or migrate to a safer country, or escape poverty. All at little cost to the quantity or quality of the seller’s life.

Why should policy interfere with such a trade? This act benefits the organ recipient as well, so it makes all participants better off. Most real world examples are less extreme, but the same principles apply.

One possible objection to legal organ markets is that some people might sell out of desperation, against their long term interest. A reasonable response is to require informed consent, rather than banning the organ market.

A second possible objection is that only the rich will benefit from legalized sales. That is unlikely, since the increased supply of organs due to legalization will drive organ prices down. Plus, private or public charities can subsidize organ purchases for low income patients, while keeping the trade legal to foster greater supply. Government funding for organ purchases might even pay for itself by improving recipient health and reducing public expenditure on health care (e.g., dialysis treatment for kidney failure).

Thus a legal market for organ sales would have the key feature of other markets: voluntary exchange that benefits both sides of the transactions.