The poor and their health. Can they sell it?

In a post entitled Should the Purchase and Sale of Organs for Transplant Surgery be Permitted? Gary Posner wrote

Another set of critics agree with me that the effect on the total supply of organs from allowing them to be purchased and sold would be large and positive, but they object to markets because of a belief that the commercially-motivated part of the organ supply would mainly come from the poor. In effect, they believe the poor would be induced to sell their organs to the middle classes and the rich. It is hard to see any reasons to complain if organs of poor persons were sold with their permission after they died, and the proceeds went as bequests to their parents or children. The complaints would be louder if, for example, mainly poor persons sold one of their kidneys for live kidney transplants, but why would poor donors be better off if this option were taken away from them? [emphasis added] If so desired, a quota could be placed on the fraction of organs that could be supplied by persons with incomes below a certain level, but would that improve the welfare of poor persons?

Steve Landsburg made a similar point in an article about a woman who was taken off a ventilation machine because her family couldn't afford it. He says that the cost of lifetime insurance against this sort of thing might be $75 at age 20. But he says,

Tirhas Habtegris would probably have taken the cash. Then she'd have gotten sick and regretted her decision. [But why not ask people what they would prefer?]

We outlaw selling oneself into slavery. I think there is a similar argument to be made here. But these are intelligent people asking serious questions. I'm taken aback not to feel sure about my position.