So the outrage over "workers rights" is delayed until Uber can no longer exploit them?

To add onto this —- living with only one kidney rather than two only barely increases your risk of dying, and many people each year die due to lack of kidneys. So, creating a market here (regulated of course) would save a lot of lives.

>> I'm an adult, if I want the money isn't it strictly better than I have the freedom to cash in on my human resources [by selling my kidney]?

> Yes.

By this logic, slavery should be legal, because people should have the freedom to sell themselves into it (for instance, to purchase medical care for a loved one).

It's a commitment device.

Sometimes it can be beneficial to you to remove your own options- if you can prove to others that you've removed that option.

For example, look at the prisoners' dilemma. If both prisoners were able to commit, ahead of time, to not defect, this would be better for both prisoners. By removing a choice, and proving you have removed that choice, you actually get a better outcome than what would be possible if you could choose to defect.

This applies in asymmetric situations, too, like contract negotiations given a significant imbalance of bargaining power. It can be beneficial to the worker to, say, prevent themselves from ever agreeing to work in unsafe conditions, even if the boss offers extra pay for it (which the worker might want).

Thus selling organs, or selling your children to "adoptive" parents. It's not about somebody else having "authority"- it's about you intentionally burning bridges, provably pre-committing, removing the "choice" to do things which, on a societal level, could be harmful.