Titling a thread "Should Japan ban Hollywood from anime?" and using Avatar: The Last Airbender as your example kind of implies that you consider it both anime and from Japan. xD Which it is neither. Yes, I am being ~that guy~

But, in the end, all adaptations tend to be rubbish. Blanket statement, whaaaaaaat. How many terrible video game adaptations have there been? That's right all of them. Book adaptations are often slated for being terrible compared to their source. Heck, a large proportion of comic book movies are bad. I enjoy some adaptations and not others. Some of them I enjoyed simply because they were terrible.

I don't think that this is a problem unique to anime adaptations, however I'm sure the cultural differences do not help.