Into institutionalised slavery. Sadly slavery still exists, is live and well, and occurs throughout the planet (even rich countries). The difference is that it is not statutory now in most places.
It's not like people in prison are actually all guilty of their convicted crime.
You'll see this double-standard a lot for minor offenses as well. How many times has MKHB been caught excessively speeding (including 90? in a school zone) and still have a license.
We forbid cruel and unusual punishment. If we lived by the morality you just articulated, we wouldn’t do so. I think slavery is cruel and unusual, I think that’s clear.