I've thought about that one a lot and I think it is the real intention. The admitted purpose of punishment in the legal system is punishment, not rehabilitation. That is something that can be change, but until it is, only punishments both cruel and unusual are prohibited. Unusual but not cruel punishments allow for flexibility like forcing someone to write a paper or read a book. Other punishments, like putting someone in a cage, are necessarily cruel.
This country was founded with a workforce of slaves and indentured servants, ankle deep in the blood of natives. One might rationalize with difficulty some way to argue the US isn't racist by design because of that, but to argue that it was civil libertarian is a step too far.
The civil libertarian language comes from being heavily seeded by small Protestant cults, but not wanting to fall into European-style religious wars over it. Also, ironically, to protect the rights of a slaveholding minority.
I’d mourn for the US, but it seems it’s been dead & gone longer than I’ve been alive.