Irrational to suggest Adams is racist

First, his usage wasn’t racist. He applied the word to himself, as a descriptor to be proud of.
Second, it’s contrived, straw-man nonsense to suggest Adams was equating his experiences in his era with slavery-era US. The word didn’t die out with slavery. It has a modern usage as an indicator of social prejudice in a post-WWII context. And there are social parallels. Civil rights marchers in the 1960s sang the same songs as black civil rights protestors in the US.