<p>The Avatar's job isn't to keep people from journeying into the Spirit World or attempting to contact them, he's meant to be a bridge between the two. He'd work more as a mediator between the two different worlds in major issues, such as what he did with Wan Shi Tong and the Gaang during The Library episode, not run to and fro in order to answer and figure out every little squabble people want to blame on the Spirits. Not to mention, I've already agreed that not just any random person could get in contact with them, so it's a mute point to try and use as a defense.
</p><p>The problem with that idea though is we get confirmation on how many were devoted to their ways just by looking at how many of them were benders, and why they were. As this wikia itself says, "Unlike the other nations, the people of the Air Nomads were, without any seen exception, all
benders due to the high level of spirituality of their people." Since their heightened level of spirituality is the seeming cause for their unique percentage of Airbending population, it's more than safe to assume they were all quite devoted to their spiritual beliefs.
</p><p>How exactly did I validate your point by arguing that Air Nomads aren't stupid? Your entire argument seems to be that "optimistic idealism ends up being wiped out, because they keep getting caught in traps, leaving only the outlying members of their society who for some reason are willing to change a belief system that's been in place for thousands of years because wartime always results in 100% of a surviving force turning into cold, pragmatic Lawful Evil monks who would do anything to silence a potential threat." Even if such a thing happened over a long period of time, it would happen over multiple generations of terrible things happening, not a mere 100 years. The entire concept I'm inferring here, that their idealistic attitude is bad and results in their death, is ludicrous because we have first hand evidence that having an optimistic ideal outlook doesn't keep Airbenders from being any less effective in battles. Look at Aang, who is easily on of, if not outright, the most idealistic character in the show. He manages to travel across the known globe, enduring tragedies and battles that would kill most trained soldiers of our time, almost every step of the way, and yet manages to remain so idealistic that he finds a way to end the war without killing the most powerful Firebender in existence at that point, someone who Iroh himself wasn't sure he could be beaten at all if the Avatar failed.
</p><p>All Air Nomads embody their core concepts, that's been established. You're misinterpreting the phrase "Seperating ones self from worldly concerns", and taking it to mean something radically different though. Seperating yourself from worldly concerns doesn't mean ignoring everything that happens in the world outside of your own nation. It means to keep your mind and soul pure through lack of physical attachment, to phrase it basically. This could be practiced in any number of ways, some of which we've seen on the show itself. For example, during his Earthbending training with Toph, when she starts snacking on his nuts and using his glider to crack them. He had no real problem with her eating the nuts, and even though he was hesitant and resistant to her using the glider, he ultimately allowed her to abuse it. Both of these actions are examples of seperating yourself from worldly concerns. Though Aang had dear memories for the glider, it is still only a physical object and has no bearing on the emotions and thoughts brought on by it existing. A more modern and relatable example would probably be walking out to head to work and seeing your car was stripped by thieves during the night for scrap parts. You'd most likely be freaking out and pissed, especially if it was a relatively new car, but a person who has masterfully seperated themselves from worldly concern wouldn't bat an eye, seeing it as merely a material item they never truly needed. They'd still feel the emotions associated with such an act, but they would get over the initial negative influence and instead move past it all to acceptance significantly more quickly. Now, this exact same person who gets over the destruction of their car in moments, could also see a report about a terrorist bombing and feel terrible anguish at the fact that such a thing happened, same as any other guy. According to your interpretation though as i understand it, he wouldn't even bat an eye at the death of innocents, and instead would treat it as if it doesn't affect him, even if it's in the same city he lives in. That's not Air Nomad philosophy, that's nihilism.
</p><p>War preparations don't have to, and rarely do, involve any one of those, and I know that for a fact. I've been a part of veteran assistance groups since I was 11 years old, and I've heard every story you could imagine, ranging from World War 2 to the Persian Gulf War, and every engagement inbetween. The only time the concepts of fortifying and hunkering down came up were due to the soldiers having already exhausted all means of potential escape, while defenses were something that was constantly maintained cause you could never know for sure when an enemy would attack. You don't train and practice for years on evading danger and finding a path out of danger, such as the Air Nomads would, only to resort to trying to absorb damage and outlast the enemy in a war of attrition at the first sign of violence. That would be like training exclusively in jujitsu for an MMA match, and then trying to win by exclusively throwing punches, it just makes no common sense.
</p><p>Also, to be fair, I'll answer why we wouldn't see any defensive structures. It has been a hundred years since the initial genocide, and we've seen that the Temples were on fire to the point of being considered a conflagration. Even if the Airbenders had erected defensive structures for some odd reason, between the fires capable of scorching the earth, a hundred years of mountain weather, and the Fire nation engaging a war which would mean they take all resources they can, I would have been much more surprised if there had been any remnants of the structures left.
</p><p>As a side note, why do you keep assuming Sozin's Comet was always a harbinger of doom? There would be no reason in their time to assume a mighty celestial object, which at the time was known just as the Great Comet, would herald the initial assault of a war. They had no way of knowing, nor any way of expecting, that firebenders got such a massive power boost from the comet. The only reason anyone even knows this happens a hundred years later is because Avatar Roku specifically tells Aang the comet does as such. Which only goes to show how well prepared for the war the Fire nation was, that they managed to keep such a thing secret.
</p><p>The only reason they didn't is probably because Aang ran away and trapped himself in ice at the first mention of being taken to a new Temple, away from his father figure, because he was eavesdropping. If he hadn't run away, he would have been safely in the Eastern Air Temple long before the Comet arrived, which could very well have been where any secondary plans to keep him safe would be put into action if needed.
</p><p>Would telling a 12 year old he would have to single-handedly stop an entire nation from going to war, and failing to do that, lead a battle to ultimately kill a man, really be a smart move? You can't assume that just because he's the Avatar he can handle such responsibility, he's a child whose entire life is already breaking down in front of him. They had already broken a big taboo and informed him he was the Avatar 4 years before they should have. Just from that realization, it essentially crippled his normal life to the point that airbender children ostracized somebody who was like a brother to them, and the majority of his Elders started treating him like a concsripted soldier. Even if he hadn't run away, why do you think the smart plan would be to tell the 12 year old that not only would the fate of the world soon rest upon his shoulders, but that in order to stand a chance of restoring balance he would have to try and learn and master a skill being used by the very people he's supposed to be fighting, who are most likely aiming to kill him, and are the only people capable of teaching him this skill. How, exactly, would that be a good idea?
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