The Thirteenth Amendment of the Constitution states that Slavery is illegal, with the exception of punishment for those incarcerated and convicted of a crime, meaning that slavery was never truly abolished as stated in the history books.
The petition acknowledges the events that led to the creation of the thirteenth amendment -- to avoid alienating the former Confederate states post Civil War.
However, this led to the exploitation of prisoners within the justice system, which continues 150 years later into the modern era.
There are many means to punish a crime, or to rehabilitate an individual convicted of a crime. However, to resort to slavery, an action considered immoral, as a punishment, seems hypocritical of the justice system.