Ilya Somin is very sure of himself here. And everywhere else, also.
While I agree with him for the most part, I no longer believe the issues are quite so clear cut. If someone sells an organ because s/he is desperate, that's something we should worry about.
But in any case Levy Itzhak Rosenbaum has been convicted of brokering organ sales, for profit.
Ilya Somin's strongest point, of course is this: Where's the harm? Compare the two states of the world, one where sales are allowed and the other where they are prohibited. Who is better off under prohibition? To favor prohibition you have to answer "the society," since no individual is better off.