However, are we using today's values and mores to judge the actions of past generations? I suspect that many of these artists were motivated by love and admiration for this music. I'm not sure about Jolson, don't know much about him. However the UK's Black and White Minstrels seemed to me to be by way of 'tribute'. What about G. H. Elliott, the English music hall singer? And this Emmett Miller that we've been alerted to in a seperate thread looks interesting.
Many things appear quite unacceptable to us now when we look back on them - I could give you a long list not connected to music - but I think we need to place them in the context of the times. Views on racism have changed dramatically. The Black and White Minstrels achieved massive viewing figures and record album sales - it would be interesting to do an attitude survey of those viewers now.
There was a hilarious hoax post here a few years ago (in Mr. Nagy's day) allegedly originated by a black Buddy Holly impersonator who was seeking advice as to whether he should 'white up'. It caused a bit of a stir and I'm not sure his true identity was ever revealed but I know who I strongly suspected!