I always felt that private prisons could work great, if specific incentive laws are passed. First, give the inmate a choice of which prison to attend, so they are competing against each other based on reputation. Second, if someone re-offends and ends back in prison, then the original prison housing them would be on the hook paying for their stay at the new prison. This gives private prisons an incentive to properly rehabilitate by making sure the prisoner comes out in a better situation than they went in (education, therapy, etc).