I understand people who wanted something more according to the source material.
Is this bad? No.
Is it bad because she is black? No.
Is the movie going to flop? Most likely.
Is her hair terrible? Yes, it is. (My humble opinion)
Is Disney pissing off the majority of their fans with this? Yes.
The only movie I watched from the new remakes is "Aladdin", because my wife wanted to see it, and it wasn't that good.
Dumbo, Cruella, Pinocchio, Lion King, Beast and Beauty, Mulan, Pete's Dragon, Cinderella, Lady and the Tramp, and Jungle Book, I have not seen any of them. This one looks even less interesting to me (not for the casting).
This is a business, they can do whatever they want, and yes that includes screwing up the casting, and changing the sexual orientation of characters as they please (Generally speaking). Also, Disney should be able to understand that it will bite them in the ass because most people will complain and it is their right to do so.
In my case, my brother is the one who pays Disney+ every now and then, so I really do not pay a cent to watch any of those movies, I could not pay a cent to see them and even less in the cinema. Marvel movies are the ones I watch but they have gone downhill since "EndGame", won't talk about the Marvel series, because I have not seen any of those either.
If they wanted to make a Mermaid movie, they could have made a new (story, setting, characters) movie, instead of this, and "maybe" create a hit instead of a possible financial flop, since they are pissing off people.
TLDR: You are a lazy person, learn to read.