Medical self-defense: why can I buy a gun to save myself, but not a kidney?

Tyler Cohen has links and more comments at Marginal Revolution:

Americans have historically put great weight on the right of self-defense which is one reason why many people support the 2nd Amendment, as the Supreme Court noted explicitly in District of Columbia v. Heller. But what about medical self-defense? John Robertson argues:

A person can buy a handgun for self-defense but cannot pay for an organ donation to save her life because of the National Organ Transplantation Act’s (NOTA) total ban on paying “valuable consideration” for an organ donation. This article analyzes whether the need for an organ transplant, and thus the paid organ donations that might make them possible, falls within the constitutional protection of the life and liberty clauses of the 5th and 14th amendments. If so, government would have to show more than a rational basis to uphold NOTA’s ban on paid donations.