supported the end of slavery.
Bullshit. They are calling for its return.
I've never understood why people seem to accept the premise that slavery actually ended in the US. Full on hereditary chattel slavery ended, but has anyone every actually read the amendment?
Section 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.
Section 2. Congress shall have power to enforce this article by appropriate legislation.[1]
In other words people can still be enslaved for life as punishment for a crime. There's nothing in the text that seems to prevent old style slavery of anyone you can convict of something, although their offspring are safe (until their first conviction, which is pretty likely since they would probably become wards of the state) The only real additional constitutional protection is in the 8th amendment in the bit about "cruel and unusual punishment". Given that "compliance blows" in prisons don't seem to run afoul of the 8th, the circle seems to be pretty much complete. There's nothing in the constitution preventing the sale of human beings as defacto property, to be forced to work and beaten if they don't. The health and safety standards would just be a bit higher. This, after all, does actually pretty much go on in some US prisons.