Whenever I think of Rowling and how her racism isn't taken seriously and regarded as a phenomena restricted to fandom, i think people really need to look at how racism in fiction impacts people in real life. How those stereotypes alienate and contribute to the already prevailing beliefs of white supremacy, some of them downright linked to incredibly violent phenomena.
Lavender being turned from a black girl to a white girl may seem miniscule to people who aren't black women, but you need to understand the overall issue with the negligence and dismissal black women are often given, and how attitudes and beliefs that we aren't worth it, that we're lesser than other women, has been the justification for murders, missing black women, and virtually no protection for black women. When such beliefs are replicated in fictional worlds, you see how it comes into circle when brought to the real world
It's the prolonging and platforming and exposure of an idea that dark skinned black girls don't matter that is the problem. And that was absorbed by so many young black girls when we first watched harry potter.