"Should we be singing this song??? Or should we leave it for the Klan? I'd sure be curious what folks think about this. "
I'm sure the original poster was wholly in earnest in posing the question. Try reversing the question. Would anyone suggest that we should sing nonsensical, unattractive doggerel because the saintliness of its composer demanded it?
Amazing Grace is probably sufficiently remote from its long-dead writer to be pretty-much value-free save for the words, tune and type of person singing it these days. Part of my rather limited guitar repertoire, I'm afraid, so it gets played willy-nilly. The folk process transmits and handles stuff, just like evolution.
"my lefty folky friends" - would they recognise themselves from that description? Thought the split these days was meant to be Libertarian/Communitarian, anyway.