I agree with the sentiment but it should be pointed out that even public works have to pay their workers at market rates when there are no forced laborers (so:

I agree with the sentiment but it should be pointed out that even public works have to pay their workers at market rates when there are no forced laborers (so: most of the time). Throwing a bunch of forced laborers at public works kind of screws over the average Joe that used to do that for pay. So, like you say, it shouldn't take away from the rights of others. Just pay the prisoners just like you'd pay any other worker regardless of the kind of job.