Why wouldn't a black Superman work? ...
Because he's an iconic character dude, a large visual change would just not work.
See, this is the crux of the misunderstanding between the two sides of this debate. Some of you see a change in skin color as the largest possible physical difference, outweighing all the similarities that two people might have. But I
don't see it that way, and there are other people who don't see it that way.
Superman is:
tall
muscular
handsome
square-jawed
dark-haired
blue-eyed
light-skinned
There are plenty of nonwhite men who are tall, muscular, handsome, square-jawed, and dark-haired. If someone shares those five traits with Superman
but has darker skin and eyes, I just don't see that as the same kind of huge dissimilarity that you do. It's only a difference of 2 traits out of 7. If that person is an actor who's also able to capture Superman's personality well -- to convey his strength and compassion and goodness, to do a good job differentiating Clark and Superman -- then that gives him an even larger number of traits in common with the character, so the two visual traits that differ are an even smaller factor in the equation. Like I said, we're not talking about casting a model here, we're talking about casting an actor, someone who has to capture the character's personality, not just his looks. Even aside from any racial issues at all, it's naive to base any casting discussion purely on an actor's appearance.