Depending on the reasons for it, there isn't necessarily anything wrong with casting based on ethnicity. Obviously Django and Black Panther need to be played by black men. Jasmine needs to be played by an Arab girl. Moana needs to be played by a Samoan girl. Mulan needs to be played by an Asian girl. There are movies with historical and/or geographic contexts that may not include certain ethnic groups because they are attempting to reflect a reality. None of this is wrong. As to the recent casting of Ariel, I think the lion's share of those who object, with the exception of a couple of degenerate assholes, object based on the idea that the casting choice doesn't accurately embody the character they grew up with. I would count myself in that group. It doesn't have anything to do with believing she's in any way, shape, or form inferior. You can disagree with that, fine. However, trying to claim that anyone who takes that position is some sort of supremacist is a disgusting and intellectually dishonest mischaracterization.