"Prison slave labor" is just one more component in what is affectionately known as the American prison industrial complex
. The vicious cycle goes something like this:
Every night about dinnertime, the good, hard working people of The United States watch their evening news, which parades story after story on violent, drug related crime. Corporate crime and dirty politics are largely ignored, leading the populous to over estimate the drug problem in this country.
When election time comes around, politicians display their "tough on crime" stance, to appeal to the misinformed masses. Large organizations who stand to gain from increased incarceration, such as The Corrections Corporation of America, contribute heavily to politicians who promise to return the favor by passing tough drug laws upon election.
Upon election, the friendly politician concocts some plan of legislation to protect his good constituents, maybe he passes some new mandatory minimum laws. This, in turn, increases the demand for new "correction facilities." Contracts are awarded to the same prison construction companies that contributed to the politician's campaign.
This finally brings us to prison slave labor. When it comes time for government projects, such as new construction of roadways or upkeep of existing roadways, the government saves itself money by employing the prisoners and paying them little to nothing.
It seems everyone gains from this machine except the human fuel that keeps it running, over 2 million people are currently incarcerated in the United States. All of this leads many people to say No More Prisons.