Prisons exist as a way not only to punish the perpetrators of crimes, but to prepare them to reenter society

This goal runs counter to the purpose of a private enterprise - to make money. Profits are maximised in private prisons by cutting corners - on anti-recidivism programs such as education and work skills programs, on the conditions the prisoners are kept in, to the food the prisoners are given. Poor treatment in an attempt to make more money will only serve to increase recidivism rates- making society more dangerous and enlarging the prison population. This, of course, is also part of the plan for private prison operators - this ensures a constant supply of inmates, protecting their bottom line. Even if the overt reason for ensuring a constant prisoner population is removed, the realities of private prisons are that they actively work against the purpose for which we have prisons.