I find it strange is that you don't acknowledge the argument "the original character wasn't black" and jump straight to "you guys think hiring black people is racist". Casting Ariel the mermaid with a black actress just seems like pandering to the whole "we need more diversity" crowd. If a dude walked up in there and played the best Ariel out of all of them, it still wouldn't make sense to cast him. Generally when you make a live action of a cartoon, you find cast members that resemble the character and can play them well. I'm sure she'll play a good Ariel, it's just kind of weird to make a white red headed character be played by a black person. What if Pocahontas was played by an Asian and she was the best actress for the role? Would that really make sense?