[Galin]

Originally Posted by Galenriel

Thanks, for some reason I had it in my head that the Moriquendi were, well, if not evil, not very 'elvish'. I don't know where I got that from, lol.

Here's a look at the term Moriquendi (and Sindarin Mornedhel, Moerbin) according to JRRT's Quendi And Eldar (from War of the Jewels). A long post, especially considering that I must follow with something from Of Dwarves and Men too, but we can see that it was Tolkien himself, who, at times seemed to associate Moriquendi with, well certain 'negative implications' let's say (at least from a certain internal perspective):

There also existed two old compounds containing *kwendī: *kala-kwendī and *mori-kwendī, the Light-folk and the Dark-folk. These terms appear to go back to the period before the Separation, or rather to the time of the debate among the Quendi concerning the invitation of the Valar. They were evidently made by the party favourable to Orome, and referred originally to those who desired the Light of Valinor (where the ambassadors of the Elves reported that there was no darkness), and those who did not wish for a place in which there was no night. But already before the final separation *mori-kwendī may have referred to the glooms and the clouds dimming the sun and the stars during the War of the Valar and Melkor, so that the term from the beginning had a tinge of scorn, implying that such folk were not averse to the shadows of Melkor upon Middle-earth.

The lineal descendants of these terms survived only in the languages of Aman. The Quenya forms were Kalaquendi and Moriquendi. The Kalaquendi in Quenya applied only to the Elves who actually lived or had lived in Aman; and the Moriquendi was applied to all others, whether they had come on the March or not. The latter were regarded as greatly inferior to the Kalaquendi, who had experienced the Light of Valinor, and had also acquired far greater knowledge and powers by their association with the Valar and Maiar. (...)

In the period of Exile the Ñoldor modified their use of these terms, which was offensive to the Sindar. Kalaquendi went out of use, except in written Ñoldorin lore. Moriquendi was now applied to all other Elves, except the Ñoldor and Sindar, that is to Avari or to any kind of Elves that at the time of the coming of the Ñoldor had not long dwelt in Beleriand and were not subjects of Elwë. (...)

Moerbin as applied to them is usually translated 'Dark-elves', partly because Moriquendi in the Quenya of the Exiled Ñoldor usually referred to them. But that no special reference to Elves was intended by the Sindarin word is shown by the fact that Moerbin was at once applied to the new bands of Men (Easterlings) that appeared before the Battle of the Nirnaeth. If in Sindarin an Avar, as distinct from other kinds of Morben, was intended, he was called Mornedhel. (...)

The implication that as opposed to Celbin the Moerbin were allies of Morgoth, or at least of dubious loyalty, was, however, untrue with regard to the Avari. No Elf of any kind ever sided with Morgoth of free will, though under torture or the stress of great fear, or deluded by lies, they might obey his commands: but this applied also to Celbin.

The 'Dark-elves', however, often were hostile, and even treacherous, in their dealings with the Sindar and Ñoldor; and if they fought, as they did when themselves assailed by the Orcs, they never took any open part in the War on the side of the Celbin. They were, it seems, filled with an inherited bitterness against the Eldar, whom they regarded as deserters of their kin, and in Beleriand this feeling was increased by envy (especially of the Amanyar), and by resentment of their lordliness. The belief of the Celbin that, at the least, they were weaker in resistance to the pressures or lies of Morgoth, if this grievance was concerned, may have been justified; but the only case recorded in the histories is that of Maeglin, the son of Eöl.' JRRT Q&E

Sorry for the long edited quote, but it might take me longer to paraphrase it all correctly. There's also an interesting marginal note (same book as above, but with respect to the text Maeglin) which reads:

'(...) For Eol was said to be a 'Dark Elf', a term then applied to any Elves who had not been willing to leave Middle-earth -- and were then (before the history and geography had been organized) imagined as wandering about, and often ill-disposed toward the 'Light-Elves'.

'But it was also sometimes applied to Elves captured by Morgoth and enslaved and then released to do mischief among the Elves. I think this latter idea should be taken up. It would explain much of Eol and his smithcraft.'

JRRT Maeglin

Christopher Tolkien goes on to comment that: 'I do not think that 'Dark-elves' had ever been used in the sense referred to in this note, that of 'darkened Elves', Elves ensnared and corrupted by Morgoth.' In any case, Tolkien wrote a sketch of Eol's history wherein it was thought that he was captured and taken to Thangorodrim; but he thought better of it, being too repetitive of the history of Maeglin.

Anyway, there's a later account (later than Q&E) called Of Dwarves And Men which reads, at one point:

'It was therefore modeled on the classification by the Atani of the Elves: the High Elves (or Elves of Light) were the Noldor who returned in exile out of the Far West; the Middle Elves were the Sindar, who though near kin of the High Elves had remained in Middle-earth and never seen the light of Aman; and the Dark Elves were those who had never journeyed to the Western Shores and did not desire to see Aman. This was not the same as the classifications made by the Elves, which are not here concerned, except to note that 'Dark Elves' or 'Elves of Darkness' was used by them, but in no way implied any evil, or subordination to Morgoth; it referred only to ignorance of the 'light of Aman' and included the Sindar.' The Peoples of Middle-Earth

Christopher Tolkien does not note this as conflicting with statements made in Q&E, but he does point out (in note 62 to ODAM), with respect to Tolkien's further statement that it is doubtful if any of the Avari ever reached Beleriand, that back in Quendi And Eldar there is a reference to Avari who had crept in small and secret groups to Beleriand.