I read a bit about postmodernism recently. I think the difference between yourself/Scott and the 'X studies' traditions is that they're not into classically philosophical arguments like you're making here. It's all about implied power relationships, the identity of speaker and listener are as important, maybe more important, than the content.

Whereas for you and Mr SSC, the identity is to be studiously ignored in favor of only focusing on the argument, to treat it fairly.

So everyone is using wildly different metrics and then wondering why their interlocutors seem crazy.

Rights are mostly won in a power struggle. For that, the idea of the rights has to be conceived first, and made the point of the struggle. This can be seen as "invention".

Then rights can be rationalized and tweaked a bit so that parties with comparable power do not step on each others' toes, and become allies. This can be seen, more roughly, as "discovery".

Rarely rights are granted by the more powerful to a less powerful because of moral / religious reasons. E.g. the anti-slavery movement in the US had a significant religious component, based on the idea that God created people equal.

More often a more powerful party gives a less powerful party some rights because they need an ally and want to prevent a full-on power struggle. I think women's suffrage had a significant component of this in many places.

Powerful and oppressive parties can definitely "uninvent" rights; look at any totalitarian regime for examples. Say, communist regimes often revoke the right to freely trade. Most oppressive regimes gladly uninvent the right to congregate, and usually the right to free speech. They tend to frame these activities as harmful and unnatural. Regaining them usually involves a power struggle; see above.

Frederick Douglass pithily summed it all up with “no struggle, no progress” / “Power concedes nothing without a demand. It never did and it never will.”