Prostitution is legal in my country, but it'd be mad unethical to force someone into prostitution 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.
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.
Training and incentivizing a prisoner to change their behavior (rehabilitation) has a better chance to provide a much larger gain for society in the long run.
> But fundamentally, making prisoners work is not a bad thing.
Forced labor is a violation of human rights. Either these rights are inalienable or they aren't.
At what point should prisoners do something, anything, to mitigate what damage they've done to the rest of us? Is planting potatoes in the hot sun in Texas too much to ask? Regular law-abiding folks do it after all.
And note: when folks have to plant potatoes in the hot sun as part of prison, recidivism is very low. For whatever reason, though I'd guess that petty criminals are essentially lazy and having to work a real job is more than they want to do. It changes their outlook, when prison work outweighs the benefit of petty theft etc.
There's a moral dimension (who are we to judge etc) and a political one (out-of-control profiteering). But fundamentally, making prisoners work is not a bad thing.