Does anyone else fear that privatizing prisons could lead to marketing revenge and other ills?

One of the things I locked horns about the hardest in Social Studies was the treatment of prisoners.Some wanting to put the screws to people already confined and others who thought confinement was enough.So I'm wondering if the privatization of prisons might lead to selling revenge or worse.As these officers are not constitutionally bound would they have to follow the cruel and unusual criteria set out by the US Constitution?Something down deep in me feels this might be the real motive besides cost savings.What is to prevent them?