Jack Dempsey never fought black fighters because his promoter Tex Rickard feared (white) America would react the same way after the Jack Johnson victory if Dempsey lost; with hatred for a black fighter beating another great white fighter.
I don't fault Dempsey. None of us can fathom how fucking wicked the nation behaved upon Johnson's victory. It came close to Wills vs Dempsey- but they stopped short when the question of a potential Dempsey loss was considered. If so, why would he have even sat down with the man as seen here if he was so racist as some claim?