Since the whole basis for the series, the reason fans loved it, was its Eastern orientation, this is a stupid reason to change things. Would you take Superman's Krypton or the Lord of the Rings' Middle Earth and make it black or Asian? Why not, if you sincerely believe in color-blind casting?
A couple postings demolish the arguments for Shyamalan's whitewashing of Airbender. These apply to other works of fiction too. For instance, eliminating Indians in the TV show Crusoe or casting Johnny Depp as Tonto.
Is 'The Last Airbender' Racist ... or Just Drawn That Way?
By Gary Susman
Well, context matters. All of those characters are relative ciphers, people who don't have much backstory, and what little backstory they do have isn't especially tied to their race or culture, the way it is for the main characters in 'Airbender.' Also, white people don't have a long history of being underrepresented in Hollywood films, or of being reduced to racial caricatures, or of only getting to play villains.
As for the The Wild Wild West, it was a decades-old property that no one cared about. Besides, it was so devoid of racial context that casting Smith didn't matter.
Marketing isn't the issue
By Q. Le
And who is to say Asian actors in distinctly Asian narratives are any less capable of drawing in American audiences? Ang Lee’s “Crouching Tiger, Hidden Dragon” in 2000 opened the gateways to a Hollywood flood of Hong Kong and Asian cinema that had been established by star Asian actor predecessors such as Bruce Lee and Jackie Chan.
No, most worlds start out white, and the brown ones often become white. This pattern is evidence of Hollywood's racism.
Would fans of Superman or Lord of the Rings accept their beloved characters becoming black or Asian? No, of course not. Then why should fans of The Last Airbender accept this whitewashing?
This argument flies from the ends of Shyalaman and Paramount defenders, who believe that in this day and age we should all be colorblind to race and its associated implications.
However, as presented in the PBS award-winning documentary “Unnatural Causes,” it’s been proven that ethnic minorities, compared to White Americans in the same socioeconomic statuses, have higher rates of chronic illnesses such as cardiovascular diseases and heart attacks than their white counterparts.
These higher rates are the result of allostatic load and weathering–the resultant and combined stresses that can result from differing levels of racism that are either explicit or implicit.
For more on casting The Last Airbender, see M. Night vs. The Internet: The Airbender Mash-up and Last Airbender Is "Completely Atrocious." For more on casting issues in general, see Denzel Washington as JFK? and Indians Hold Steady at 0.3%.