This is an honest question, not some Glenn Beckian prelude to a "poor put-upon white folks" rant. I saw The Last Airbender last night, and while it was just as awful as you might have heard, the color of the leads didn't really bother me in the least. Looking at the original cartoon characters, I suppose they look somewhat "Asian," but I'm not sure if Asia as we know it even exists in the world of Airbender.
I don't know whether the film is supposed to take place on an alien planet, in the distant future or in some Tolkienesque fantasy world, but wherever it was, the presence of giant flying 'n swimming Swiffer duster, some monkey-looking creature that seems like it should be She-Ra's best friend, and a pond filled with God-Koi seem to suggest that it's a world unlike ours today. So I can accept the fact that the four tribes of this strange world are a virtual United Colors of Benetton ad, with the fire, earth, air and water tribes each sporting plenty of multicultural members.
It was, I'm sure, a shock to the devoted fans to see some of their beloved heroes cast in a way that they were not prepared for, just as I'm sure some fans weren't initially ready for a black Kingpin in Daredevil, a black Nick Fury in Iron Man or a black James West in Wild, Wild West. But all three actors worked out very well; Daredevil and Wild, Wild West both had their problems as movies, but casting a white actor wouldn't have solved them.
Like I said, this is an honest question I'm grappling with myself. I'm half-Latin and I always liked seeing someone who looked more like me, or my sisters or my mother pop up on the screen. But I do think that it's somewhat unfair to espouse the benefits of color-blind casting one day, and demand fidelity to the source material the next. The part should go to the actor that can best fulfill the role, and if the director says it's these four, I think there's no reason to not take him at his word. M. Night Shyamalan treated the world and its culture reverently enough -- there were certainly no Rooney-level "Miss Go-Righree!" abominations -- that I think any charges of full-on racism is unfounded. The worst that might be said is that 'ol Manoj was a little tone-deaf in regard to how his casting would play with fans of the original Avatar.
It's a complicated issue and there are strong feelings on both sides, but I think no matter what our race, creed, nationality or sex we can all agree on one thing: The Last Airbender is one shitty movie.