In other words, you think there exist situations in which it is just to enslave people. You're trying to make a distinction that literally no one else makes because you want to separate forced labor as punishment for a crime from the connotations attached to the word slavery. It's just a sleight of hand.
As long as you allow that society has the right to force people to be locked up without their consent because they broke a law, I don't think it's a stretch to say that society has the right to force people to do work.
I don't see why that follows, considering they're two different things. In any case I do think prisons themselves are one of the blights of modern society.
While I'm not certain that society doesn't have the authority to force people to work (though, if it is ambiguous/uncertain, I would advise "don't", and I am not confident it does, so I advise "don't"), but I do agree that it doesn't really seem to follow, at least not without assuming some other premises.
