Oh and we'll most probably see Al Sharpton blowing his top off if we get a Chinese 'Blade' or Caucasian 'Uhura'.
I always see variations on this answer on boards like this, and I don't agree. Sharpton's head remained on when Angelina Jolie was cast in Wanted, taking the reins of a character that was designed to look like Halle Berry in the comic. Before Snipes and Goyer made Blade popular, he was about as well known among the general public as was the Wanted character so you can't say it was because the Wanted character was unknown. Jolie even put on makeup to play a real-life biracial woman, Marianne Pearl (sp) in a film, and Sharpton has not spontaneously combusted.
Sharpton also somehow managed to hold it together when black characters were switched out of new BSG, both Tigh and Boomer, two significant characters. And the one black replacement, Dualla, was a minor character. Or when McFarlane made Terry a white character back in the Spawn film because there were studio concerns that a majority black cast would make the film a 'black' film and it would not be as profitable. Or when a very fair Rachel Weisz (sp) was Nefertiti in the Mummy Returns.
Whitening of roles isn't as bad as it probably was back in the day, with stuff like John Wayne as Genghis Khan, but it still does occur and there are no civil rights protests about it like you and some other people claim will surely happen if previously black or non-white characters are played by whites.