Just this, too, in short(-ish), because it could rapidly become disproportionally time consuming :
If Lord of the Rings is a fairy tale, then practically every work of fantasy is a fairy tale.
Yes, this is more or less my point.
And you miss it if you shift to a technical usage of "fairy tale". This would be like discussing animal rights with a biologist who goes "but scientifically humans are animals". Or discussing racism with an anthropologist who'd go "but this isn't racism because it's not about a race" - which anthropologists usually don't answer (outside a zealously pedantic first year) because they know in which context which broad/narrow/popular/technical usage of the word is the most relevant to communication.
The point here isn't academic textual classification, discussing whether the Hobbit belongs to some oral tradition, or whatever. The relevant thing is that such fantasy tales are processed by the public like they process fairy tales : it's a series of magical premises that aren't debated, a "this creature was evil" is self-sufficient, just like any fairy tale defines a "good king" archetype, a noble "prince charming", an "evil witch". These do not operate on rational real world logic, this logic is suspended like in front of a myth, which importance resides in structures, articulating abstractions (good, evil, stepmotherness, etc). There is a pointless geekery in seeking mechanisms or content beyond the puppets that have been set up by an author : smurfs have no sexuality and no reproduction, they simply "are", and biological coherence is irrelevant to their imaginary universe. What hasn't been thought up by an author in their universe isn't to be "discovered", it's simply a hollow place that stays hollow because what matters to the story is on the envelope's level.
Of course, any cultural production comes from the author's culture and individual beliefs, so there is always a worldview to find and deduce from a text. But again, this worldview is expressed in dreamlike logic, in little touches that don't have to make an exhaustive and coherent system (few fictions would function if they had to be exhaustively logical), and even less be an actual reflexion of the real world : in many fictions, even pseudo-realistic ones, human races exist and determine mentalities, or homosexuality is a sign of weakness and perversion, or women are less capable than men, etc... These premises make stories (and character ehaviours) that fall apart if analysed in terms of real world analogies, or even in terms of inner logic (because these concepts -like the concepts of ghosts, vampires, zombies, etc- simply don't work if you overanalyse them). The fictional universe is structured differently than the real world, and doesn't require full logical consistency, it exists "as described", plot holes and contradictions included.
There's a geeky habit of trying to bring fiction to reality-level of cohesion (one hilarious archetypal example was aliens nerds debating for years to rationalize biologically the difference of design between the first two movies - while the real answer is how cool it looked to different directors). It can be a fun creative mind game, but it makes no sense to treat it as a revelation of an original work's hidden reality instead of a fan-created addendum. Just like inventing stories where dracula is some ("humanized", "realisticalized") tormented lovestruck soul, adding pyschological complexity to orcs is an example of this : it expands an universe into another, fan-created around the first. Even if it's to include "more logical", "less fairy-tale-ish" things to it. Less, I say it, "childish" things.
Because yes, Tolkien had fun expanding and expanding on his stories, and took its own methodology very seriously, but it's still toying with lego (even if of the technic variety). His beliefs and worldviews seep in, but these are not, again, objective duplicates of the world (he can have a overly simple vision of it on some aspects, complex on others, and he may be selective about which complexity is relevant), the root of his work is some lovely little tale for kids, and -as far as I know- it's also documented that his world is shaped by his childhood impressions of nature, of african and english environments, which give the his descriptions their haunting, poetic impact, this universal resonance. It's a very emotional component of his writing, no matter his later rigorous cosmogony/history constructions. And it also works because of some key lack of explanations or details descriptions. Precisely, orcs are vague (imagine how many details a Stephen King would have described), they are catch-all boogeymen, like ogres in fairy tales, about which all you need to know (be told and take as granted) is that they are terrible. They are the bad.
Now you're free to make of them what you want in your own headcanon or in your own fanfictions, or independent works. Just like vampires can be romantic conflicted souls or one-dimension predatory revenants. In fact their vagueness (and relative abstraction) is also what allows projections, and efficiently universalizes them. But inserting components of your own (in their "hollowness") and declaring this to be some underyling objective truth is wrong. And useless. Complexifying them is interesting, but this complexification doesn't have to be presented as something inherent to that work. It's an extension in its own. Like, say, Tournier's own personal take on Defoe's Robinson.
But not every fictional character (or creature) has a revealing psych-analysable childhood. Most of them are just structural functions. Single ideas on legs. Heck, sometimes even stories that mean to say truths work better with abstractions and reductionisms. After all, myths and fairy takes do convey messages about the human condition that are often valid. And they convey them through minimalist, technically false, impossible, reductive components. Like a proverb would. "Fleshing out" a tale isn't necessarily a path to increased accuracy. It depends on what its grammar demands.
(Also, I and most of my friends have read Tolkien during childhood. I don't think it's a work that belongs to an age bracket, but it does have something childish to them and I really mean it in the most wholesome, noble sense of the term. I think it describes a world with a sense of marvel that gets lost with age. And capturing it, indirectly capturing/transposing childhood awe and anxieties, makes a large part of its power.)