It is misleading to refer to the US prison system as privatized, when the percentage of the total inmates that are in private prisons is only around 3% [1].
Privatized prisons do create a huge moral hazard, but currently the pro-prison groups with the biggest scope and influence are probably police/guard unions [2] and the "tough on crime" crowd.
[1] http://www.globalresearch.ca/the-prison-industry-in-the-unit...