The clear environmental message of these film is a bit too on the nose of me but whatever but I really can't stand how the message is betrayed by the story. The problem for me is that the Navi live in a environment without any real worry because the stupid planet supercomputer makes sure that the biosphere remains in balance. Humans don't have something so convent but it's even worse than that. We developed civilization as a way to survive in a harsh world where death is around every corner, overconsumption is just an unintended consequence of successes.
You can contrast the Navi with Humanity but presenting the Navi's way of life as superior is completely retarded unless Cameron thinks we should go back to living like savages. Someone should remind him that we don't a planet god or USB hair if he thinks that's a good idea. What Avatar needed was more balanced, not everything about our way of life is bad. Sure, we may have driven the mammoth to extinction and are addicted to oil but those infant mortality rates are looking pretty good, people don't die because of a cut and we can feed millions of people.
I read some spoilers for the franchise that may or may not be true. The Navi aren't savages, they are actually super advanced and the whole planet is their creation. They've just been larping as stone age hunter gatherers. Fantastic, the message now is that science can solve all your problems but science doesn't exist in a vacuum. Civilization and infrastructure are vital to progresses and the film straight up tell us how important the mining is the the future of Humanity.
Pandora clearly is meant to evoke Gaia as a concept. But you are correct, humans did not build civilization on a world with some sort of collective conscious that would both protect them and also prevent ecological devastation.
Perhaps an unintended message is for you to exist in harmony with the earth-not only must you live a stone age existence, but a super computer or deity is necessary to actually keep the system at peak harmony. While there are Gaia proponents in real life that argue this-no one actually thinks there is a sapient will that defends the earth's ecology and keeps it in a state of healthy growth and stability.
Ecological "balance" is not some new agey magic where everything is hunky dory-what that really means is none of the component parts devour the rest, predators die of sickness and competition, prey get eaten, natural cycles occur at such frequencies as to not disrupt the entire system, and so forth, organized chaos. Any of these countervailing elements could in certain circumstances overcome the others-but the system keeps itself by the multiple elements in constant competition at certain tempos and conditions.
Watch any nature documentary-"natural" life is ruthless and pitiless. You must either be the fastest gazelle or you get eaten, or the fastest lion or you starve. Either way you die and decompose, and the circle of life continues.
No wonder then that humanity built civilization to strive against and overcome the eternal battle royale that nature really is. We just ended up devastating the planet in the process. On Pandora-the struggle of life is mediated, its savagery tempered by a god that cares.
TLDR: Pandora's ecology is much gentler and less savage than what the RL "struggle of life" really entails. Humans have to deal with nature that cares not-where a mistake is not forgiven, where prey and predator must constantly outrun the other, where sometimes all you have to do to go extinct is just be a little slower, a little dumber, a little weaker. We overcame this, the Na'vi do not.