Thanks for the write-up! I'm familiar with Cash's version of most of the songs on the album, but haven't sat down and listened to the album from beginning to end. Will give it a spin. Bitter Tears is another great album in a similar fashion of protest, this one about Native Amercans/Amercan Indians.
Regarding the point that "no one used the term cultural appropriation at the time", of course they didn't say cultural appropriation as such, but the idea that black music is not for white people to sing is not a new one. Woody Guthrie held the belief that blues belonged to black people, and while he had tremendous respect for it he actively encouraged white folk singers not to play it (his exception is in We Shall Be Free, which he performs with Leadbelly). Peter Seeger (who disobeyed his orders and played the blues anyway) talks about it at some point, but I can't find the source right now.
Of course, Woody would also borrow left and right, but in his musical style he never imitated his contemporary blues artists.