[davem]

Child, First, I suspect that For Tolkien 'Faerie' (as we see in 'Niggle') is 'the best introduction to the 'Mountains', if we understand 'faerie' in the way Tolkien himself understood it. Its the 'gated world' we step into first - as the Hobbits step into the Old Forest, the 'folk tale' world, before moving on to the 'gated world' of legend & myth, & finally on into the ultimate (& only truly 'ungated' world - because it contains all the 'worlds' that may exist within itself - the 'mountains', or The Undying Lands, West of West.
But, back to the plot! Maybe what we're seeing in all these 'gated worlds' is what Tolkien accused the Elves of - embalming. You bring your own little world to a state of (what you consider to be) 'perfection', then you want to 'embalm' that 'perfection', so it can't change. Is it really a fear of death? - Tolkien said LotR was about 'death, the inevitability of death' (which issue has been dealt with in another thread I started, so I don't want to go over old ground). Why the desire to close yourself off from the world? Is Elvish 'embalming' of the world a statement about their attitude to death, their 'contempt' of it, a way of 'casting it from their world'? The desire to preserve anything in a state of what we consider 'perfection' is to prevent its death. Maybe we're on this same ground again. Death is the great enemy, always coming, always needing to be watched & combatted. But Tolkien knew the truth (after the Somme how could he not?) that 'The Dragon' would come, inevitably, however bravely you fight to hold on to what you care about, & even that ultimately all you can do is fight it, in the right way, because its about how you live, not the fact that you'll die.
Perhaps what these 'gates' are intended to keep out is not 'men' or 'Elves', but 'The Dragon', Death. But the Dragon can't be kept out. I think its significant that by the end of Lotr, when we've read the Tale of Years, we've seen the death or passing of all the characters. From the Prologue we know that all the events of the book happened long ago, & all those people's & places have passed from the world. What I think Tolkien is saying is that, however big the wall, however strong the gate, it will never keep out the Dragon. But there is stil hope (even if it is, as Tolkien said, Hope without guarantees), & there is also the chance (or the obligation?) to live as well as we can, for as long as we can. We can fight, even if we're only 'fighting the long defeat'.
Finally, would everyone stop saying, they're not up to joining in this discussion! I didn't go to college, I'm just someone who's read a load of books & spent time thinking about the kind of subjects dealt with here. I'm far from being an intellectual giant! I just throw in a few thoughts which strike me. I'd hate to think there were people out there who are maybe keeping really interesting ideas back because they think theyre not 'smart' enough to join in.