It is involuntary (all punishment is!), but it's not servitude in the same sense that slavery is. If you want to call that "slavery" nonetheless, that's up to you, but you'd be equivocating. There is a difference between slavery as an institution of unjust forced submission and "slavery" as just punishment for crimes committed.
The fundamental issue is that the majority (or the oligarchy) decide what is "wrong".
I seriously doubt (and see no evidence for the idea) that the US is so lawless that we can have almost a quarter of all prisoners in the entire world while only having a fraction of its population.
This speaks strongly to the idea that huge amounts of wrongful imprisonment occurs and (as a logical consequence) these people are slaves against their will without their having done anything worthy of punishment.
> There is a difference between slavery as an institution of unjust forced submission and "slavery" as just punishment for crimes committed.
The difference is solely the standing law. During the nazi regimen (godwin's law, but really) many of the appalling things they did were legal. It was legal to execute, and it was legal to do forced labor.
Slavery was always legal, that was the problem all along! A slave could not physically escape without the fear of unpunished retribution.
Slavery doesn't mean "unjust forced submission", it means "forced submission". There was slavery before 16th C Atlantic triangular slave trading, there's legal and illegal slavery, and maybe there's ethical slavery too (or maybe not).
Redefining the word so that prison slavery doesn't qualify seems obtuse, counterproductive, and doesn't even have the defense of being historical.
