she isn't white either. she's a mermaid which is a made-up creature and it doesn't really matter what color human plays her in the moving pictures because either way it's got nothing to do with realism
casting a black person as a historical white person would be dumb but not really worth talking about either
In my opinion it really depends on how the work is marketing itself
I think it's dumb if a work is trying to pass itself off as accurate or authentic, but works that are clearly taking massive liberties with what actually happened don't really need to worry about how similar an actor is to the figure they're portraying. No one cared when Hamilton cast black actors for Aaron Burr and Thomas Jefferson because the play is clearly trying to have fun with history. Obviously they weren't rapping at the first Congressional Congress. A lot of the events of Hamilton's life that the play depicts were different from what actually happened, and that's totally okay because the play is trying to be fun and entertaining first and foremost (Granted there are plenty of little historical Easter Eggs and factoids sprinkled in throughout the play, but still). So if someone's
actually upset that the actor's skin color doesn't match the figure they're portraying but are completely okay with all the other liberties the play takes, then they're probably just an actual racist being disingenuous and feigning concern over historical accuracy
But on the other hand, what
is dumb is something like the Netflix series Cleopatra, which makes a big deal in its marketing about how accurate it was for casting a black woman as Cleopatra who historically was of Greek and a bit of Persian descent. And the thing is, there
were black Pharaohs. Egypt existed for thousands of years and had all sorts of different dynasties ruling over it at different points, and during at least one period the dynasty ruling over it was from Nubia. But nah Cleopatra is more famous, so they picked her and then made a big fuss about how their depiction was historically accurate and the "true" story of her life. It's telling that the main group who got pissed over this miniseries wasn't really "woke culture war" types, but instead
actual Egyptians mad at how their history was being depicted. I honestly feel bad for the actress who got caught in the middle of all that.