The most successful political propaganda in our time was convincing millions of people that caring for others and the planet was somehow a threat to America.
As long as they enjoy (forced labor) it, then it is not slavery is not a very good argument. Even outside of prison wage slavery is a real problem. Having someone work in prisons for decades and then released with barely anything to show for it is the very definition of exploitation. Likely leading to more recidivism since without the capital crime is the easiest way to support oneself after missing out on society for decades.