There is one rhetorical arguement about a shared fundamental - ownership. In this case of your body. If you can't do what you want with it then somebody else owns it. If somebody else owns your body - you aren't free you are a slave." Not owning something isn't necessarily a bad thing - not being able to own the river or air is an acknowledgment of commons - bodies far less so.

Regardless of the merits of the first arguement in the US legal system the Orwellian euphemism "unfree labor" a.k.a. slavery is allowed for convicts certainly qualifies as "close to slavery" in the same sense prebellum Southern plantations are - direct participants. I would call the statement harsh but true contextually.