Exactly. Both are simultaneously true.

Personally, I've always thought racists would struggle to get a kick out of this film, as the Klan don't turn up until about halfway through, and the film is a bloody long haul at three hours plus. The presentation of the Klan as heroes is so preposterous and absurd as to be almost comical, though I do understand the sensitivities involved, given US history.

Anyway, yes, I do think The Birth of a Nation is profoundly offensive (obviously), and yes, I do think it should be taught in cinema history classes, as ignoring it is wilfully ignorant in my opinion. I don't do Orwellian cancellation, and history has to be taken for what it is, not airbrushed, or we fail to learn from it.