Well the thread title is more than unfortunate. If were black and I read the title 'Are racist, but traditional, songs OK?' I'd probably assume folk music wasn't for me. The answer to that very baldly stated question is screamingly obviously 'no'.

"Some folks here seem to think it's a song that merely mentions race (Black Girl), and some folks (I'm one) think it's what's said, or implied, about people"

The point about a song like 'Black Girl' is not that the song is inherently racist, it's that it is inappropriate for a white person to sing its lines. A black person can sing the line 'black girl, black girl, don't lie to me', but it's just crass for a white person to, because it immediately has a different power dynamic, way too many other implications.