I don't care what Na'vi think they're fighting for, they have already lost.
At the start of 1st movie, they didn't know what lying was. Now, after 2 movies, they are backstabing each other, lying their asses off, running around with LMGs and using modern military strategies. And the trailer for A3 implies outright faction war soon.
They are fully human already. There is nothing noble left of them.