I get the idea of expanding a lot of the movies with actors of a variety of races, but I guess I don't like changes to known characters just for the sake of changes or to mix in colors. Regardless of what anyone says to me it would be weird to have a black Batman [or in this case Hermione], but it would also be weird to have a white Storm.
The harm to you, though, is zero. The societal benefit is not. So, hey, who cares if you find it weird? Societal change requires a period of transition; we all just have too deal with things feeling weird. Just like the real-live Downton Abbey type people had to deal with their first black Lords, or the UK had to deal with its first female Prime Minister. Fictional characters are harmless, and pointless, and help lead the way. They can, and should, utterly be sacrificed to the societal benefit.
I think we're at the point where it's safe to ridicule people who object to skin-colour based casting. Anyone who considers skin colour in a different way to how they consider eye colour or hair colour needs to just shut up at this point. Is Steve Rogers blond or dark-haired? Is The Doctor English or Scottish? Is James Bond white or black? Is he blond and English, or dark-haired and Irish? Or equivalent characters from your country? Is Batman really Welsh? Is Superman really English? Is Spiderman English? Is Robin Hood American? Or Australian?
These things don't matter as long as the actor does a good job.