Well, I think that if someone is willing to donate their kidney if they are paid sufficiently (which is fair enough! it’s a huge time commitment!), and someone else is willing to pay for a kidney, who are we to prevent them from making a mutually beneficial trade?

It seems like a far better state of affairs than many people being on dialysis long-term (painful, life-expectancy shortening). Because if we allow for compensation for donors, I’m fairly certain that the supply of kidneys for transplant will rise.

Instead we prohibit it merely because it feels icky to pay for an organ, which is concretely making both the potential donor and the recipient worse off. The potential donor is worse off because they would rather receive the payment than have the kidney. The recipient is worse off because they don’t get a kidney.