Give me your kidneys!

Uh...this is not what we had in mind

As noted, the problem isn't people challenging the wishes of their departed relatives. It's that their departed relatives do not communicate those wishes in the first place. Or don't have them. If you look at the countries which went this route (a sort of nudge policy), they don't end up with many more kidneys out of all those dead folks who had to say no affirmatively instead of say yes anyway.

Really the problem with the US kidney donor market, the cause of the shortfall between donors and needed kidneys, is: that there isn't a market. Kidneys can be harvested from people who have recently died. But not everybody dies in such a way that their organs can be put to this use. Kidneys, unlike many donated organs, have the advantage of being able to be donated and used by giving one off while still alive. Meaning the shortfall (and by extension the expense of getting a needed kidney), is best made up by people giving one of their kidneys to someone who needs it. One way to do that is to provide an incentive for people to "donate". That is: to allow people to sell their kidneys (create a market to trade kidneys). Which is what Iran does as that outlier out ahead of us on live kidney donation.

I suppose we have that issue of people thinking that doctors would be too eager to harvest organs (or poor people would somehow be too eager to sell them), and thus risk a backlash that would reduce the amount of kidneys available. I think that if the prices, as we would expect, go up in the event of such a backlash, such a market would stabilize. And this would not become a problem.