Obviously this - via Friend of the Blog Llama God - is brilliant in every way. The absolute tip-toppymost of "fanwank" (a disgraceful term for so rewarding a hobby). I'm not sure where the idea comes from that there are enough Great Eagles to take on the Nazgul, and it's not like Mordor didn't have any ranged weapons or the ability to put trolls at every entrance to Mount Doom, but as an answer to "why not use the eagles?" it's supremely well-crafted.
Except... why is everyone so dead set on the eagle flight idea in the first place? To me the response to why it was never tried was always obvious: the Great Eagles are sentient creatures just like men, Dwaves, Elves and Hobbits. Why on Middle Earth would we assume they'd be any more resistant to the One Ring than Boromir or Saruman were? Hell, everyone was pissing their chainmail boxer shorts over the idea Sean Bean might grab the Ring and start causing trouble. Can you imagine how screwed Middle Earth would be if a giant flying predator with talons that could rip an elephant into steak tartare decided it was time to become an invisible master sorcerer?
"Hey Gandalf, I just realised we could have flown eagles to Mount Doom and saved us months of exhausting travel and dangerous encounters!"
"Hey Frodo, I just realised the brutal dictatorship of an unstoppable flying magic bird of prey would fucking suck!"
It's a much less pretty theory than the one at Tickld, I grant you, but it has the advantage of treating animals smart enough to speak both English and Moth (and man would I have loved to see that scene - "What's that, Mothie? Little Gandalf's trapped up a tower? SQUAWK!") and show up to battles for the freedom of civilisation as something more than glorified private planes. Talking animals deserve our respect, even if in this case I'm asking that we respect them enough to be terrified that they might succumb to temptation and become our ruthless avian overlords.