The truth is that giving convicted prisoners opportunities to work is probably a big net positive. I'm sure plenty of them would work for pennies rather than rot in a cell.
The root of the problem is if there is injustice in sentencing or coercive work conditions. Not the work itself. But that requires far more investigation to establish than pearl-clutching about the universal practice of "forced labor".
But if there is a legit criminal behind bars, I would like to hear reasons why they shouldn't be able to work in a highly controlled, safe workplace.