Hey, I meant potato farming. Regular people do it voluntarily. Its not even all that onerous, just hard work. Don't know where that 'prostitution' bit was supposed to be going.

The fact some people will do something voluntarily doesn't mean it's ethical to force other people to do it against their will.

Therefore, it's irrelevant whether "regular people do it voluntarily" - because it's the being forced against their will that's the ethical issue here.

One illustrative example of this maxim is prostitution.

But isn't that deliberately ignoring the fact we're talking about prisoners? Not citizens with full rights? So 'making them do something' is the entire point of the exercise.

Its not advancing the topic to exclaim breathlessly about loss of rights, when that's the point of prison. We could be talking about misaligned incentives or effectiveness etc.