The party(s) haven't been duly convicted.
You keep squawking about "slavery", in order to distract from the "or" clause: "involuntary servitude".
Imprisoned, not "duly convicted" and forced to pay "road agent" rates to the private monopoly comes under the heading of involuntary servitude [involuntary servitude is a United States legal and constitutional term for a person laboring against that person's will to benefit another, under some form of coercion other than the worker's financial needs.] Someone labored to produce the money to pay off the monopoly.
You're hoist by your own post, PAR35.