Speaking as a once-fan of Avatar: TLA (The TV show, not the movie. Though I love JC's Avatar as well) I have to say one of the big reasons I decided to say "Fuck the movie" was because part of my pathetic youthful innocence was based around the fact that, aside from the slight subtext of racial discrimination (In the show, the whites were the evil guys trying to rule the comparatively darker world) was the fact that race was never really made into an issue with a sledgehammer in the show, like it often is in other forms of media, was refreshing. Hell, once I got over my obsession with the fandom, I still find the show enjoyable to this day (sans the final few episodes, with the annoying Deus Ex Machina ending).
Then the movie came along. For one thing, it was M. Night Shyamalan, which in itself made it bad. But the fact that the good guys had been given to an all-white cast, while their opponents were remade from Nazi-esque white supremacists (in subtext only, of course) were of comparatively darker skin tone. It seemed like such an injustice that the motley crew of protagonists from every group in the show had been reduced to the "Light vs Dark" of every other movie.
It just felt so unjust that I never made an effort to see the movie, even considering I've watched both the Twilight movies (For the lolz! I swear! And one of those wasn't negotiable). Bob's point about minority actors having a comparatively small role in Hollywood today is completely true. Especially considering the general opinion that "Our audience can't cope with a non-white, non-hetrosexual protagonist" (this is especially true in action movies, I've noticed)
If there's anyone who bitched about the actor selection for Thor (which was awesome, by the way) on this forum, I invite you to burn in hell. Most comic book series were started in an age where racial prejudice was still widespread, and as comic book fans are easily the most bitchy fans on the planet, retconning characters to fit a more diverse culture (Like the less-American Superman, or the less-conservative Captain America) is very difficult. The increasing trend of casting minority actors in previously white comic character positions, especially considering the highly-idealized nature of many comic universes, is not the end of the world. I dare you to find a legitimate reason that such a casting shouldn't happen.