The most important question that arises from this is the question of whether private companies will treat prisoners poorly and/or may be less conscious of security as a way of making more money.
Those who argue for private prisons argue that the private sector can run prisons more cheaply and efficiently. However, the profit motive that would give the private companies an incentive to be efficient would also give them an incentive to cut corners. If a private company cuts corners, both prisoners and the public could be endangered. Prisoners could face harsher and more dangerous conditions in prisons run "on the cheap." The people could potentially be in danger if cheap private prisons had lower levels of security and allowed more escapes.
Privatizing prisons brings up the specter of prisons run shoddily so as to make more profit for the companies that run them.