I mean they essentially allowed slavery to exist for prisoners with the 13th amendment [1] -- Americans seem to view the prison system as anything goes punishment instead of rehabilitation:
[1] "Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction."
Also allowed without conviction. Those in county jails who are unconvicted are allowed to be subject to small amounts of slavery the US Supreme Court has previously ruled.
[1] "Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction."