Edit - Hmm a downvote for an on topic opinion? Would it have been better had I said "Who cares about the details its a freaking movie and you nerds need to get over yourselves?" :)
Sentience isn't an 'event'; it's not like some apes woke up one morning a few million years ago, and just somehow knew to make spears and hunt. It happens slowly, starting with the use of naturally occurring tools, like chimpanzees do with sticks, or certain octopi do with coconut shells. Some birds use rocks as tools.
Tool use evolves up from there, but if we look at our own species as an example, it probably doesn't ever really stop.
The Na'vi are probably more like echoes of human beings at an earlier point in our evolution, with the added property of having an intrinsic physical link to the environment around them. If the ecosystem ties directly into your CNS, you're going to think real hard before engaging in widespread destructive behavior, because you know first-hand how painful the damage is. So things like mining, which gave humans metal, would take the Na'vi longer, because they'd want to find a way to do it that won't cause them a ton of pain.
But they'd get there, and since Cameron is talking about sequels, the next installment may very likely show how contact with humans has pushed the Na'vi on to a more rapid path of technological development.
And your post really doesn't deserve to be downvoted, so it got a +1 from me. Come on, we're discussing the science fiction in a movie. :)
My trek knowlege is pretty poor, but I want to say this is the history of the Vulcan. They're extremely advanced technologically, but choose to live a simple life. Unlike the Na'vi, however, they don't shoot animals with neurotoxin-covered spears, growl at things that make them angry, or try to fight a war against people with guns using the aforementioned spears.
The Vulcan are one of the most technologically advanced civilizations in The Federation. If the Na'vi were an advanced race that chose to live simply, dealing with the Humans wouldn't have been a problem for them.
It is one of the very few scenarios where a war between different civilizations would be interesting: one where the technologies are so different engagement is almost impossible and you simply can't tell which one is more advanced. I think Starship Troopers explored this idea very well: there were planets humans were not even aware they were bug colonies. All weapons are designed making certain assumptions about their target. If all assumptions are wrong, the weapon is very ineffective. You can't use a torpedo to sink a mountain.
I didn't watch the movie, but from what I saw, I gather human technology can barely function there due to the magnetic fields of the gas giant and/or its moon. It's likely the technology evolved in such a place would be very, very different from ours.
The Vulcans were one of the most technologically advanced civilizations in the Federation, but not any longer, you haven't been keeping up.
This one does not seem to fit the story as portrayed. Lets put aside the fact that "a better way to live" is likely be highly subjective and assume that they choose to live in tune with nature despite the ability to develop advanced technology.
As long as they remembered this fact, that they deliberated put aside technology, they would have behaved differently towards the humans. They wouldn't have needed the marine to show them how to blind the clearing machines, they would have already known. They surely would have at least debated pulling out the old tech when their soul tree was threatened even if they finally chose not to. And they likely would have approached the humans to try to teach them their ways and show them they were "better", or if they wanted to be isolated they would have had the knowledge to be more effective in driving the humans away which they didn't even seem to try to do until the humans attacked them.
Of course you could assume they forgot, but that seems implausible. A technological civilization that choose to abandon their technology should have little problem making sure that the message of deliberately eschewing technology and why would be passed down. If they didn't their descendants would be likely to start the cycle all over again a few generations. Also, their soul tree would be likely to hold this knowledge if no other method was passed (as I mentioned in a different post, the limits of the trees information storage and transmission are never made explicit, but it seems very likely it would have that particilar piece...)
After the fall of the Roman Empire that part of the world involuntarily fell into a dark age, that is very different from intentionally eschewing technology. And those societies did rediscover most of the lost knowledge and began progressing again.
Presumably a society with advanced technology that did something as drastic as getting rid of all of it would have left behind reasons so that their ancestors would also avoid it, or at least be able to make an informed choice. It would not be hard to ensure that endured (barring a major catastrophe) for many generations.
It could have taken the form of oral histories which can be preserved (at least in general intent, even if details change) for very long stretches, or maintaining writing even if it was restricted to their spiritual leader caste, or even one remaining piece of technology in the form of an extremely durable recording that speaks to them on set anniversaries.
Giving up technology is very different to losing it as a society collapses into a dark age from a combination of corruption, war, and other factors.
Also, the Roman Empire did not have anything to function as an ancestral memory. While it has been mentioned several times before that the limits of the Soul Trees function as an ancestral memory were left vague, it seems likely that something as fundamental as deliberately eschewing technology would show up at least as echoes of an aversion to technology.
Maybe not for them. Since they are so connected via the network, there maybe a higher level of consensus.
They wouldn't have needed the marine to show them how to blind the clearing machines, they would have already known.
Not really. Why would it have been obvious to them that the things on top are what the operator uses to see anything? Even if they had technology as or more advanced, there is no reason to believe it would follow the same paradigm as anything we think of.
Overall, I think the idea that they don't feel the kind separation from the planet that we do is the most plausible reason.
Possible. You might be able say that for them living with technology might be unambiguously better. But when it is said as a simple statement by itself it appears a highly subjective opinion, or at least very dependent on the circumstances.
Not really. Why would it have been obvious to them that the things on top are what the operator uses to see anything?
A good point and a possibility, but the humans had been there for years. If they had had advanced technology of a different kind, that exposure to the humans technology would likely have let them start figuring out how the human's technology worked, even if they avoided it.
Overall, I think the idea that they don't feel the kind separation from the planet that we do is the most plausible reason.
That is certainly a possibility. I find it more likely that they simply were at the bow and error phase of technology and had not yet grown beyond it in any direction more likely.
On a more metaphorical level, the film seems to explore the contrasts of networked vs hierarchical approaches to social organization mumbles about information ecologies and development strategies