Lovecraft is interesting in that regard. His racism is so interwoven with what makes the books good, that there is no real way to read one without the other.

It is far more problematic with authors where the trait that is later "discovered" always seemed like an alien stain in their work. E.g. someone who wrote all about freedom and equality, but has some weird misogynistic moments in the books that everybody glossed over before, but now they stain the whole idea..