Adolf Hitler was a painter and Kim Il-Jong directed movies. Neither of them was any good, but if they had been, would it really make sense to judge their art in isolation, without the slightest mention of the authors’ tyranny and mass murder?
Griffith made movies that he fully intended as Ku Klux Klan propaganda. That is not in doubt. At the same time these movies are also important technical achievements and milestones of cinema. It’s not “loathsome and cowardly” to point out his racist message.
A similar problem exists with Leni Riefenstahl, the photographer and director who exulted Hitler, as well as many 1960s European leftist directors who uncritically worshipped Mao. They all should be seen and criticized in context.