Unobtanium is not 'vital' to the survival of humanity, human's aren't an endangered species in Avatar. It's just incredibly useful, if it was then maybe they would destroy the Na'vi, but I don't think they'd really want to nuke their supply location. What's not clear (maybe it will be once I finish reading the scriptment) is if the Na'vi are the only intelligent aliens ever discovered in the Avatar world. If they are, I can't imagine whatever governments remain on earth would okay the mass slaughter of them.
The oil thing is interesting, this latest war is among the most 'jaded' in recent history, but this plot was in place long before this war, and it's motives may echo the movie, but the movie predates the war. There are no false truths being paid to the humans while the RDA rape Pandora.