The purpose of imprisonment is to punish criminals by depriving them of their liberty. As a side-effect, society benefits because a criminal has been forcibly removed from visiting further misery on law-abiding people.
Imprisonment is and should be a deterrent punishment - it is not a support group.
One can both be in favor of abolishing for-profit prisons and also in favor of severe deterrent sentences for law-breakers. Profiteering private corporations naturally seek to maximise the number of prisoners in their facilities, because they are paid per inmate - so they have every incentive to ensure future "custom". This motive naturally conflicts with deterrent imprisonment - the whole idea is to forcibly prevent criminals from breaking the law again.