I think the reason that Tolkien left it vague is that he was a gentleman who knew when not to discuss something in too great a detail.
There is a quote (regarding the speech of the orcs) in which Tolkien states that it was actually more foul than he had reported, but in the interest of decency he sanitized their speech.
Given the reactions of many even in this thread, can we blame him? There are some subjects that deeply upset some people, and rather than blatantly inflicting those subjects on his readers, he was gentleman enough to hint darkly and let it be.
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...down to the water to see the elves dance and sing upon the midsummer's eve.
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