Fandom, so long divided by bitter (and stupid) pairing wars, has largely united to call bullshit on the shocking (but not actually surprising) whiteness. This gives me hope for Avatar fandom.
This post is not really for my own thoughts on the matter, because everyone else has said it better. Instead, it's to collect relevant links and get them out there.
Exhibit A: A letter-writing campaign for those of you who are angry enough to want to do something.
Exhibit B: Various explanations of why this is just not right.
Taking a show where the cultures and the world that the characters all hail from are clear, blatant, confirmed analogues and amalgams of a diverse variety of various Asian cultures, where the characters have Asian names, where their magical martial arts styles that are the expressions of their very souls are Asian martial arts, where every single written word is actually IN CHINESE and then casting white people to play the main characters is offensive.
To shorten drastically a longer rant I actually already had brewing in my head, situations like this are exactly why I think, "well, maybe he was the best actor for the part" and other "colorblind casting" notions are such specious arguments.
They're specious because they assume a world where the default setting is actually neutral, rather than being so far up the ass of "white, straight male" that Hollywood will not only assume a white, straight male lead unless there's a "reason" to do otherwise, but will cheerfully rewrite the race/ethnicity or gender of fictional characters and even of real people to assure a white male lead.
What does this casting choice say to me, the angry Asian man? It says that every time somebody speaks more slowly and loudly to me because they assume that English isn't my first tongue, they're right to do so, because I'm not normal. It says that when my freshman year roommate thought that the delivery guy calling with my order was my dad, I shouldn't have been offended, because the guy sounded Chinese on the phone, so how was he supposed to know, right? It says that every time somebody asks me to translate a random set of pictographic characters for them, they're right to do so, because I know ancient Asian secrets. It says that when Rosie O'Donnell said that Asian people talk in alternating tones of ching chong ching chong, she wasn't being offensive, because we really do all sound like that. It says that even though Konietzko and DiMartino took pains to articulate themes of diversity and multiculturalism, all their work was for naught, because people don't really want to look at people who look like me. It says that every time somebody thinks of me as the other, they're right, because I am.
Don't even tell me they couldn't find enough English-speaking Asian teenage actors to play four measly character leads in the first movie. They recruited Zuko from a band for heavens sake.... It follows that if they got Asian leads, they'd have to have Asian supporters since the respective nations were pretty homogenous, but you know what? Mel Gibson rounded up enough people of color to play an ancient civilization in Apocalypto--DO NOT tell me they don't have a comparable amount of Asians wandering around out there who'd be happy to traipse about in costume on a Hollywood picture. They managed to do it for Xena, a mid-budget made for television New Zealand-filmed production that took place in fake-Japan and fake-China for a mere couple of episodes!
Exhibit C: Relevant icons and my favorite pick-me-up out of the whole mess.
Final thoughts: the presence of Jesse McCartney on that list is just so ridiculous that it makes me hope it's all a hoax. But it's gotten as far as Entertainment Weekly, so that seems unlikely.