Outsourcing the operation of prisons presents more conflicts of interest than other contractual arrangements (e.g. R&D, construction, or IT) between government and private firms. While private prisons aim to maximize profits, they're often forced to choose between the needs of their inmates and the needs of their shareholders.
The correctional system should be geared towards rehabilitating people, not just punishment. But, we have a system that thrives on high incarceration rates because it's good for business. Instead, we should have a system that is aligned towards and celebrates lower rates of incarceration.
It should come as no surprise that officials found that private prisons are both less safe and less effective at providing correctional services. I'm glad that today the Justice Department is taking a step in the right direction by pledging to end the federal use of private prisons.