You say that Buddhism opposes things that disrupt the natural order. From my point of view, whether you donate an organ out of compassion or sell an organ out of greed doesn't matter in terms of what is natural. The result is the same, the action is the same. The only thing that differs is the motivation. Can Shih-fu explain further?

SHIH-FU:

If your point is that Buddhism is more concerned with the motivation of an action rather than whether the action is natural or unnatural, then you are correct. More emphasis should be placed on the motivation ─ whether it be greed or compassion ─ than on what is natural or unnatural.

If you donate an organ purely out of compassion, in order to save the life of another, and if a doctor is reasonably sure that you will survive and live a normal life after the operation, then Buddhism supports this action. But if it's done for monetary gain, then Buddhism opposes it. Likewise, if a woman offers her body to bear the child of another, and it's done unconditionally, then it's acceptable. But if she turns her womb into a hotel room, then Buddhism is against it.

If you give up an organ and do not accept money, but believe that later on you'll receive karmic merit for your actions, again you are mistaken, because your motivating factor is still greed. You are still thinking in terms of a business transaction.