@Joe: I can't find the exact quote now, but Berlin once told a reporter that "American composers are not Negroes, but of Russian birth and ancestry and of pure white blood."

EDIT: Apparently it was "Our popular songwriters are not Negroes, but of Russian birth and ancestry and of pure white blood."

So yes, very iffy. It might have been a way of getting people to accept him writing in different styles and different voices because there was apparently pigeonholing going on back then, as in "You're an X, so you can only write 'X' songs and not Y." Also, I think some groups of people were seen as impossible to assimilate.