As for as i know, he was always very praising about Jack Johnson and ranked him higher than Jeffries and anyone else that later came along. He started the ring magazine in a time of extremely strong racism. How could he get away with supporting a black fighter so blatantly and still have a very succesful magazine as well as being a famous writer on boxing?
Some of the more liberal newspapers of the period suported Johnson. While general opinion was verry much against him, it was possible to suport him and he had a good few white closet fans.
Chris, Ring Magazine rated black fighters long before Jackie Robinson played baseball in the major leagues. In fact if you were black before the 1920's boxing was one of the few sports open. Fleischer did not take a lot of heat for parsing Johnson in his boxing reports. Johnson created his own heat with his outside the ring activities.
In part, probably because the most ardent of racists didn't get Ring magazine - so their blind hatred wasn't readily fed into by the works of Nat Fleischer. That and the fact that Ring's existence came about after Johnson was no longer a threat to the Heavyweight title.