^^ Just my two cents on the Khan/Cumberbatch issue....
I'm less inclined to view the original casting of Khan as much of a progressive victory. To me, watching "Space Seed," Montalban's Khan, with his artificially darkened skin and noticeable Mexican accent (in spite of the character being from the Indian subcontinent), embodies (whether intentionally or not) a lot of paranoid white stereotypes about Latinos -- that they are "exotic," that their sexuality is more pronounced and overpowering, that they are a temptation to white women and sexual rivals to white men. Khan's seduction of Marlina is perfectly in line with these stereotypes. He is the threatening Other with dark skin who wants to steal "our" women and take over "our" land.
Meanwhile, one of the STID filmmakers' goals was to use the familiar character of Khan to explore the role of a rogue terrorist, as understood in our modern society, and to explore the question of how society should react to the threat of terrorism. This necessarily involves using some of the iconography of terrorism from our modern society, up to and including vessels crashing into sky scrapers and destroying them. Had Khan been depicted as a person of color, this would have played into more modern stereotypes about Arabs and Muslims -- the scary brown man come to kill our military and blow up our buildings.
So while I completely understand being upset at a white actor playing a character who is supposed to be a person of color, I'm also a bit more forgiving of it in this particular instance. This version of Khan having white skin lets the filmmakers use the character without playing into some very vile, racist tropes against Latinos and Arabs.
I absolutely don't support the whitewashing of characters of color that, as Christopher
notes, has become so prevalent. (Casting a white man to play Tonto is particularly offensive, as Tonto is a good guy, so why can't a Native American play a hero in a major motion picture?) But in this particular instance, I can forgive it.