Do you happen to know where in the letters this appears?
I have found something close in Letter 177 (to Rayner Unwin dated 8 Dec. 1955.) "Edwin Muir, reviewing The Return of the King in the Observer on 27 November, wrote:'All the characters are boys masquerading as adult heroes....and will never come to puberty.....Hardly one of them knows anything about women.'"
To which Tolkien replied:
Blast Edwin Muir and his delayed adolescence. He is old enough to know better. It might do him good to hear what women think of his 'knowing about women', especially as a test of being mentally adult. If he had an M.A. I should nominate him for the professorship of poetry-a sweet revenge.[A footnote about the poetry professorship [at Oxford] states that it was vacant at the time and nominations were being made for his successor. W.H. Auden was elected. He's the guy who said "If someone dislikes it [LOTR], I shall never trust their literary judgement about anything again."]
I'm not sure why that would be a sweet revenge (but then, sometimes I'm a slowcoach!)
Men don't know anything about women either until they've been married for a while...or so I've heard. ;) And isn't that the best way to learn?
Of course, I have no right at all to speak on the subject, but that's never stopped me before. :o
Thanks for looking in the letters. I'm almost sure that in there somewhere is a passage directly related to defending the actual survival of most of the heroes. I can't seem to find it either, could I have read it somewhere else?
I'm wondering if the defense involves Tolkien's thinking that the main theme of LOTR is death, or that the background for LOTR, the Silmarillion (which I haven't read) contains so much tragedy.