After the composed and often wise Elves we meet in The Lord of the Rings, the dangerously passionate Elves of The Silmarillion can come as quite a shock. I've seen more than one meme contrasting the Elves of the First and Third Ages. When we learn how bigoted many of the Elves were towards Men and Dwarves alike, calling Men "the Sickly" and "the Usurpers" among other charming names, and calling the Dwarves "the stunted people," and hunting them as if they were animals, it can come as something of a disappointment (S 91, 103, 204).
In The Book of Lost Tales we find the earliest evidence for the prejudice against Men, and its roots may be very deep indeed. The first indication comes in "The Music of the Ainur," when Rúmil, the Elf who tells the tale, comments on some of the differences between Elves and Men.
Lo! Even we Eldar have found to our sorrow that Men have a strange power for good or ill and for turning things despite Gods and Fairies to their mood in the world; so that we say: “Fate may not conquer the Children of Men, but yet are they strangely blind, whereas their joy should be great.”
(LT I 59)
Now to be fair to the Elves in The Book of Lost Tales only one group of Men is loyal to the Elves and they pay dearly for it. I mean of course the Men of Hithlum, led by Húrin. His son, Túrin, also sides with the Elves, but his is a complex and troubled legacy. Tuor is also from Hithlum, but unrelated to Húrin at this early stage of the legendarium. Together with his wife, Idhril, he leads the survivors of Gondolin to safety. Their child is Eärendil. (Keep in mind that at this point Beren is an Elf, not a Man.) It's also true that by time Rúmil is telling the tale, thousands of years later, Men and Elves are still in conflict with each other. Blindness may not seem such a terrible thing to accuse them of under the circumstances.
But in The Book of Lost Tales the prejudice of Elves towards Men predates not only their first meeting, but even the awakening of Men. For when the Elves wished to pursue Melkor back to Middle-earth, Manwë tried to dissuade them.
... he told them many things concerning the world and its fashion and the dangers that were already there, and the worse that might soon come to be by reason of Melko’s return. “My heart feels, and my wisdom tells me,” said he, “that no great age of time will now elapse ere those other Children of Ilúvatar, the fathers of the fathers of Men, do come into the world—and behold it is of the unalterable Music of the Ainur that the world come in the end for a great while under the sway of Men; yet whether it shall be for happiness or sorrow Ilúvatar has not revealed, and I would not have strife or fear or anger come ever between the different Children of Ilúvatar, and fain would I for many an age yet leave the world empty of beings who might strive against the new-come Men and do hurt to them ere their clans be grown to strength, while the nations and peoples of the Earth are yet infants.” To this he added many words concerning Men and their nature and the things that would befall them, and the Noldoli were amazed, for they had not heard the Valar speak of Men, save very seldom; and had not then heeded overmuch, deeming these creatures weak and blind and clumsy and beset with death, nor in any ways likely to match the glory of the Eldalië.
LT I 150
That last sentence, which I have italicized, is hardly a flattering portrait of the Elves, and the narrator here in this tale, "The Theft of Melko and the Darkening of Valinor," is another Elf, Lindo. By this time in the story Melkor had been working for some time to estrange the Noldoli (Noldor) from the Valar by insinuating that the Valar had brought the Eldar to Valinor in order to use them as unwitting slaves and to cheat them of their god-given birthright, the world itself. Now Melkor's lies bear fruit, as hearing Manwë about the destiny of Men and the need to give them time to grow, Fëanor puts 2 and 2 together and, quick as an internet conspiracy theorist, comes up with 5.
“Lo, now do we know the reason of our transportation hither as it were cargoes of fair slaves! Now at length are we told to what end we are guarded here, robbed of our heritage in the world, ruling not the wide lands, lest perchance we yield them not to a race unborn. To these foresooth—a sad folk, beset with swift mortality, a race of burrowers in the dark, clumsy of hand, untuned to songs or musics, who shall dully labour at the soil with their rude tools, to these whom still he says are of Ilúvatar would Manwë Súlimo lordling of the Ainur give the world and all the wonders of its land, all its hidden substances—give it to these, that is our inheritance."
(LT I 151)
Of this speech and its consequences, Lindo says:
In sooth it is a matter for great wonder, the subtle cunning of Melko—for in those wild words who shall say that there lurked not a sting of the minutest truth, nor fail to marvel seeing the very words of Melko pouring from Fëanor his foe, who knew not nor remembered whence was the fountain of these thoughts; yet perchance the [?outmost] origin of these sad things was before Melko himself, and such things must be—and the mystery of the jealousy of Elves and Men is an unsolved riddle, one of the sorrows at the world’s dim roots.
(LT I 151)
In this Lindo echoes something he had said previously about the early days of the darkening of Valinor: "Nay, who shall say but that all these deeds, even the seeming needless evil of Melko, were but a portion of the destiny of old?" (LT I 142).
It's easy to see the pride and prejudice of the Elves here, and maybe hear a distant echo of it in Gandalf's remark that the Elves, too, were at fault for their poor relations with the Dwarves (FR 2.iv.303). It's also easy to get the feeling that the sundered paths of Elves and Men begin in the Music itself. What I find most interesting, though, is the way both Manwë and Lindo struggle to understand why things are this way and whether it will prove a good thing in the end. They don't have answers. They have questions and they hope that this evil will be good to have been, even if it remains evil.