You don't speak for "all Americans".
A number of Americans (>1) see their imprisonment as a modern form of slavery, one that is explicitly allowed by the US Constitution:
The U.S. Constitution bans slavery except as punishment for a crime ... In Texas, some prison farms are located on the same land as former slave plantations.
It's "meaningful" in that they feel (with good justification) that they have been found guilty by a system designed to single them out and that they are railroaded into a lifetime of unpaid servitude.You may disagree with their feelings, but it remains that your blanket statement:
> No American feels enslaved in any meaningful sense of the word.
is false