Being in prison is a punishment. what goes on in prison should be designed at keeping the incarcerated in and meet their civil rights; the idea that active punishment is justified speaks to a different mentality.
This mentality is the outgrowth of "us-vs-them", but most people are closer to being "them" than they really know. If you've gotten behind the wheel of a car over the limit 3 or more times, in most states, you deserve to be prisoner.