Well, we are running into some issues about what is 'canon' and what isn't in the Avatar universe. A lot has been said here and in the hype about the movie (and I think that it also states in the "Avatar Survival Guide") that things are really bad on Earth and that the unobtainium is vital to humanity's survival. Now if that's true, then I side with Imperator and the RDA. As members of the human species we have a duty to survive and if we have to kill some of the Na'vi and destroy some of Pandora in order to survive then that's what we do. There are no moral issues besides survival. Indeed, all morality is based on what's best in order for a society to survive. Just hard luck for the Na'vi. HOWEVER, there is absolutely nothing in the movie that confirms this unobtainium-is-vital-to-Humanity's-survival theory. The only thing that is ever said is when Selfridge states that they are on Pandora because the unobtainium sells for $20,000,000 a kilo. If it were truly a matter of survival I think Selfridge would have reminded Grace of that. So, if it's just about the money, then moral issues do come into play. Is it moral for the RDA to kill members of an intelligent species and steal their land just to make money? Is it moral for Japanese and Norwegian whalers to kill a possibly intelligent species to dismember their bodies to make money? The answer to both questions is no.
So, the RDA is going to be hard-pressed to justify sending a huge military expedition back to Pandora. Especially if the unobtainium can be gotten elsewhere. We have no idea what society or government is like back on Earth in 2154 (2158 by the time they get the news) but if public opinion still has any power at all (and it might, witness what's going on in Egypt right now) there could be a great many people demanding that we leave the Na'vi alone.

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