Deterrent to future like-minded scumbags.
If you already live in hell outside of prison then prison won't feel that bad. Could even feel better because it's like a dopamine detox. I'm talking here about prison not like it is depicted in Hollywood, with rape and no protection from assault. I'm talking about prison as it should be, enforcing a near monastic lifestyle where the detained has no distractions from their own conscience and can contemplate their predicament