People are paid to be blood donors routinely and people have sold their organs for cash. No doubt it is crass. A traditional ethicist would argue that such a donation is not voluntary but coerced by the economic need of the donor. However consider the motivation of an unpaid donor. Does the gift really satisfy the donors need to be recognized as doing good or some other self gratifying emotion? Does a voluntary donor have a “psychological need”? Why should behavior motivated by economic gain be excluded but not other forms of self gratification? Finally the prisoner as a potential donor is an interesting dilemma. Truly an organ donation for freedom is easily seen as coercion. Yet if it is not mandatory,original sentences are not affected (although they ultimately might be) and non donors are not punished, why does a prisoner not have the right to make a decision that the prisoner views as being in his or her best interests? It is very difficult to parse the motivation for human behavior.
This is touched in the “ARM” stories with a cop named Gil. Those who kidnapped and killed people for organs were called “organleggers”.
What’s ironic though is that in Niven’s stories, running multiple red lights got you executed because you deliberately put others at risk. We have a society reluctant to kill murderers - but not innocent but inconvenient people.