It all depends on the context or time period in my opinion. A movie set in New York today could feature a broad mix of ethnicities and nobody would bat an eye because it's the reality of the city. Now if you were to make a movie about Iceland in the 1100's and the cast is all black it wouldn't make sense, or a movie set in China during the Ming dynasty and everyone is white. They kinda did that with some ancient Egypt movies which is bullshit but I really don't care that much, I just won't watch it if it doesn't seem good. If I do watch a movie and it is good but still features things like that it just takes away from the experience, if they're going for accuracy they're failing but maybe they aren't?