For profit (private) prisons have become big business in the U.S. Inherent in this business model is that profit is dependent of how many people they incarcerate, how long they are incarcerated, and little they can spend on each prisoner. This has resulted in these companies lobbying to pass laws that criminalize more behavior, longer sentences, and worse prison conditions. In some cases, this has even resulted in judges being bribed to incarcerate the innocent. Not only is this a clear and demonstrable threat to liberty but it has increased costs which, of course, are borne by the taxpayers.
See http://www.aclu.org/prisoners-rights/banking-bondage-private-prisons-and...