Is there nuance that can be added? Sure. Pretending one thing is the same as the other is not, in my opinion, a nuance that furthers the discussion.
It's really, really hard to equivocate the 13th amendment to, say, the EPA rules overturned by Michigan v EPA, or any of the other thousands of regulations imposed last year.
The 13th Amendment ended slavery by regulating away the property rights of slaveholders and so I can understand that libertarians are a might bit peeved about this reduction in their freedom to own other human beings. I offer my condolences.
The obvious rebuttal being that "laws" allow for the military draft, which is also slavery, or jury duty, which is an admittedly much milder form of the same thing, or the internment of the Japanese, or the infinite detention in Guantanamo, but since you probably already know that libertarians wouldn't be on board with slavery in the first place and are just positing up strawman after strawman, I think it's fair to assume that your arguments aren't being made in good faith, so I'll leave you to it.
