I understand the point you're making here, and I've certainly seen plenty of "fan fiction" theories taken far too seriously in discussions of Tolkien. But for my own pride's sake, I would attempt to draw a distinction between those "fan theories" and the sort of analysis that we used to do on the Tolkien Usenet newsgroups (including rec.arts.books.tolkien, which inspired this article: I was involved in conversations with the article's author on this topic back in the '90s).
The attitude adopted by much of the r.a.b.t community was a deliberate echo of Tolkien's own: we treated Middle-earth as an independent "sub-created" world (to use Tolkien's term from "On Fairy Stories") which ought to have "the inner consistency of reality". In such a vast imagined history, there are obviously huge gaps in our knowledge where Tolkien never told us what happened or why. But in a few rare cases when those gaps are closely connected with the story that Tolkien did tell, we can make a strong case for a unique consistent way to fill the gap (or at least a "very likely" answer).
One of my favorite examples of this was a longrunning collection of debates related to the blades that the hobbits got from the Barrow Downs and their effects on the Nazgul. I won't say we reached consensus, but after years of related discussions quite a few of us had reached the conclusion that those weapons had some sort of enchantment making them especially dangerous and frightening to the Ringwraiths. And then, unexpectedly, a previously unpublished excerpt from one of Tolkien's essays was quoted in Hammond and Scull's Reader's Companion that explicitly confirmed our conclusion (and much of the related evidence that we had gathered). It felt for all the world as if a scientific theory that I had helped develop had just been confirmed by experiment.
It's that sort of thing that encourages me to think that we were one step more rigorous than fan fiction. [And shameless plug: I still maintain the newsgroups' FAQ site. It doesn't say much about the Eagles question, but here's the full story on the barrow blades that I mentioned: http://tolkien.slimy.com/faq/History.html#BarrowBlades ]
Filling gaps is a perfectly fine exercise, and can even lead to consensus when the gap is small and you take years of discussion to fill it. The question of Sauron's anti-air detection and defense capabilities within Mordor, and of the Council of Elrond's confidence in assessing these capabilities, is much larger, vaguer and conducive to controversies. Not to mention that the character most likely to propose using the eagles (Gandalf) was also the most aware of any possible impediments (e.g. Sauron being able to conjure storms and blinding lights at a moment's notice etc.).
The attitude adopted by much of the r.a.b.t community was a deliberate echo of Tolkien's own: we treated Middle-earth as an independent "sub-created" world (to use Tolkien's term from "On Fairy Stories") which ought to have "the inner consistency of reality". In such a vast imagined history, there are obviously huge gaps in our knowledge where Tolkien never told us what happened or why. But in a few rare cases when those gaps are closely connected with the story that Tolkien did tell, we can make a strong case for a unique consistent way to fill the gap (or at least a "very likely" answer).
One of my favorite examples of this was a longrunning collection of debates related to the blades that the hobbits got from the Barrow Downs and their effects on the Nazgul. I won't say we reached consensus, but after years of related discussions quite a few of us had reached the conclusion that those weapons had some sort of enchantment making them especially dangerous and frightening to the Ringwraiths. And then, unexpectedly, a previously unpublished excerpt from one of Tolkien's essays was quoted in Hammond and Scull's Reader's Companion that explicitly confirmed our conclusion (and much of the related evidence that we had gathered). It felt for all the world as if a scientific theory that I had helped develop had just been confirmed by experiment.
It's that sort of thing that encourages me to think that we were one step more rigorous than fan fiction. [And shameless plug: I still maintain the newsgroups' FAQ site. It doesn't say much about the Eagles question, but here's the full story on the barrow blades that I mentioned: http://tolkien.slimy.com/faq/History.html#BarrowBlades ]