Sorry, but if he adapts a TV show that features people of colour as the main characters, then he has a responsibility to cast actors of colour in all of the primary roles.
He has a responsibility to
try, yes. But trying doesn't guarantee complete success. Ideals are things to be striven for, but they can rarely be entirely achieved. You can try your best to cast inclusively but still not be able to meet your goals, because there are a lot of other factors you have to balance.
Here are some cogent comments from writer-producer Zack Stentz (
Andromeda, Terminator: The Sarah Connor Chronicles, Fringe, Thor), who is himself Lebanese-American, by the way:
http://www.exisle.net/mb/index.php?s=&showtopic=63922&view=findpost&p=1303771
I'm very sympathetic to diversity in casting, both for ethical reasons and practical ones (particularly when you're casting soldiers or other people who dress alike, it can be really difficult for audiences to tell characters apart if they're all the same ethnicity.)
But I've also spent time actually casting projects, and it's really easy to throw stones at someone for not casting the "correct" ethnicity or believing that he or she just didn't look hard enough when you haven't done the job yourself. Because the simple fact of the matter is that for a lot of reasons, the talent pool you have to work with is different sized for different ethnicities, ages, and degrees of able-bodiedness. And you simply have a lot more choices if you cast a character as white (or to a lesser extent, black) than if you limit yourself to Asian actors.
That doesn't mean you should[n't] try your hardest and press your casting director to beat the bushes and look beyond the usual suspects for potential candidates. But often times directors look at literally hundreds of candidates for an important role before finding the right person for it, and the difference between almost right and right actor can be narrow but critical in the success of a project.
So again, while diversity is a laudable goal and should be pushed for hard, I wouldn't be so quick to dismiss a director claiming that he or she had to look beyond a preferred ethnic category to find the right actor.
I don't have a problem in principle with individual characters being cast by actors of different ethnicity. I didn't have a problem with Billy Dee Williams as Harvey Dent, Dean Cain as Superman, Kristin Kreuk as Lana Lang, Samuel L. Jackson as Nick Fury, or Bernie Casey and Jeffrey Wright as Felix Leiter. I don't have a problem with the new Sulu being Korean instead of Japanese, the new Uhura being Afro-Latina instead of African-American, or the new Spock being Italian instead of Ukrainian.
We also have:
*Jake Gyllenhaal as a 'Persian' in the upcoming
Prince of Persia
*Characters in the
Dragonball film being changed to white characters, etc...(Similar to what is going on in
Airbender).
*Ving Rhames as Kojak
*Danny Glover as Philip Marlowe
*Michael Clarke Duncan as Kingpin in
Daredevil
*Will Smith as Jim West in
Wild, Wild, West
*Years ago, Tim Burton was thinking about having Marlon Wayans as Robin for one of the
Batman films.
Granted, some of these films or tv shows I sited sucked; usually, if the film is good, you won't have much said about the characters and the changes.
And, I didn't know Spock was Italian...I thought he was Vulcan?
And Uhura is African-American? (I thought she was
African?)
Not every black person is
African-American, Christopher...

So I can live with the characters in The Last Airbender being of different ethnicities than the ones in the cartoon, as long as the casting process makes a fair effort to be inclusive -- as long as people of all ethnicities are free to compete on an even footing and be selected on the basis of their merits rather than their appearance. Equal opportunity isn't about guaranteeing success, it's about guaranteeing a fair chance to compete. And as long as the process is fair, the results should be acceptable, even if they fall short of our hopes.
And overall in this movie we've got mixed-ethnic Air Nomads, East Asian/African Earth Kingdom, South/Southwest Asian Fire Nation, and Caucasian/Russian Water Tribe -- I think that's reasonably inclusive for a film cast in the United States. (They could've done better if they'd cast it in Asia, but finding enough really good actors fluent in English would've been a problem.) It's just as diverse as the animated series, just with the specifics coming out differently. Maybe it doesn't seem that way as much in the first film where the focus is more heavily on Aang, Katara, Sokka, and the Water Tribe, but in the next two films we'll see a lot more major characters from the Fire Nation (Azula, Mai, Ty Lee) and Earth Kingdom (Toph, Bumi, Long Feng, the Earth King), so that will balance it out more.
In fact, it could be argued that excluding white actors from consideration altogether would be just as bad as excluding nonwhite actors. The goal should not be to meet some quota for each race. The goal should be to cast fairly.
That's one point of view. I'm pretty sure, depending on the ethnicity, background...you have various points of view on the subject.
You're right, it
can be argued. However, as we see there are still
casting issues going on.
I saw a film at my school directed by a visiting independent gay Asian-American filmmaker called 'Fruitfly' not too long ago. A lot of what this filmmaker put in his film possibly would have been changed to make it 'marketable' if this was a studio film...i.e. tone down the gay aspects, give the Asian female lead a white boyfriend, change the Asian characters to white, etc....
On the other hand, you have other films such as
Our Family Wedding which (despite if it's good or not) feature a cast of primarily Latin performers with African-American performers. Too, whenever we see an 'interracial' film...it usually is with a white character and a non-white character.
I personally found (and have heard in discussions, and read in articles) that Asians are usually deemed as 'foreign' so it is usually claimed that there can't be Asian performers found....which is obviously ludicrous. (I almost spelled that 'Ludacris')....
We've had the film
Better Luck Tomorrow which featured a predominantly Asian-American cast, directed by Justin Lin who went on to direct
Fast and the Furious sequels...
So, I guess my point is, there are still strides to be made....