> If the point is to make the men work, then pay them a fair wage.
I agree they should be paid a fair wage. They should be given a bill for their housing and their debt to society and their victims which they can pay off with their wage. The vast majority of prisoners owe society (and their victims) more than they could ever hope to earn in a lifetime.
The whole idea of being a prisoner is to take away rights of someone who have done harm to others. This is done by taking away his freedom (i.e. by locking him up in a prison cell), taking away his right to vote (in many countries) and removing his right to freedom of association.
Locking a prisoner up is not the same as kidnapping (since you make false equivalences). Since a prisoner’s time is already wasted (by locking up in a cell), that time could just as well be used for something productive.
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You know what is slavery though? Forcing the taxpayer to pay for the housing and maintenance of a criminal. The taxpayer doesn’t have any say in the matter and doesn’t have a choice. Each person in jail had a choice.