Avatar: Cameron's manifesto
Of course, I wouldn't use the word harmony to describe the relationship some natives are perceived to have with their environment in our world. In reality, the relationship is one of oppression, based on keeping the native population in check. This also explains why natives (be that the Na'vi in Avatar or some bushmen in Africa) have little use for precious minerals lying beneath their "sacred" lands.
To be more specific, the relationship with nature is one of death, famine and an endless stream of deadly diseases. The population size is kept constant so that there's no need to build megacities, not to mention spaceships. It is only after this "harmony" is broken that man is able to break free from the oppression of his environment and of his tribe where individuals are delegated to roles they were chosen for by their elders (or some imaginary beings).
This oppression, or harmony, is not anyone's choice. It's merely a sad state of affairs. An individual wishes to preserve his or hers genetic heritance. Pumping out as many babies as you can, hoping that one or two of them reaches maturity is not ideal considering the opportunity costs of being nothing but a birth machine which is why we desire to improve our living standards so that we can settle for a smaller number of children. To get around this oppression, we discover ways to exploit our surroundings, to cultivate land. This results in production surpluses. We end up having countries instead of small and isolated tribal areas which are far from ideal from a genetic point of view; problems such as inbreeding depression result from low levels of genetic variation.
Since living in that state of oppression is not a choice, it's only stupid for people to perceive this primitive way of life as something that is much closer to man's true nature. It's usually echoed that Western people have lost their touch with that something magical in the dirt and have embraced techno-consumer culture instead. Of course, that "something magical" is nothing but ignorance. Having lost this ignorance does not make us Westerners any poorer but richer, both materially and spiritually. Science and magic cannot co-exist. Pockets of superstition and oppression such as Indian tribes or Islamic neighborhoods cannot exist where the West rules.
And then there's imperialism. We are to believe that Westerners only brought tears and sorrow to the darkest corners of the world while in reality we brought technology, education and, ironically, the means (agricultural technology, food aid and modern medicine) to maintain surplus populations in 3rd world countries, populations that would not exist without Western aid. (This wouldn't be such a bad thing if 3rd world economies were liberalized in order to end this dependency. Aid, however, only provides an excuse not to liberalize.) Of course, property should not be taken by force (although property rights of extraterrestrials have not been defined: would we consider aliens as animals, comparable to dogs and cats instead of humans?) as in the movie, not when it's already being utilized by the natives.
Even worse, in the film imperialism is mixed with modern American politics. America never was an imperial nation (except for their sole possession, the Philippines). The film makes references to America's post-9/11 foreign policy, mentioning well-known concepts such as "pre-emptive strikes" and "shock & awe". In the movie, marines are used to further commercial interests, pushing the ridiculously simplistic view that the Iraq War is/was about oil. This only hurts the credibility of the movie and it's totally unnecessary. (The same thing happened with V for Vendetta.)
As a 3D experience the first half of the movie was incredible but the story (its premise was copied directly from Unreal) turned out to be so repulsive, predictable and naive that I was in great pains watching the second half. No wonder: Cameron's political views have been well known since at least Aliens but while Aliens is a brilliant movie with subtle reflections on human nature, Avatar is an in-your-face type of political manifesto.