I should mention that there are several passages where Tolkien describes Morgoth as a sexual predator (to go back to that term). In the Lost Tales, Gothmog is his son, and the mother is an ogress....well, she's certainly not Morgoth's wife, so one could infer that she wasn't entirely willing/happy about the situation, but we don't know any details. Then, in the Lay of Leithian, when Luthien dances before Morgoth, he gives her a speech about, essentially, how he is going to break her like trampling on flowers. I mean, you can read into it what you will, but it seems pretty straightforward that he is threatening/promising to rape and murder her.
'And here of need thou shalt remain
now, Luthien, in joy or pain-
or pain, the fitting doom for all,
for rebel, thief, and upstart thrall.
Why should ye not in our fate share
of woe and travail? Or should I spare
to slender limb and body frail
breaking torment? Of what avail
here dost thou deem thy babbling song
and foolish laughter? Minstrels strong
are at my call. Yet I will give
a respite brief, a while to live,
a little while, though purchased dear,
to Luthien the fair and clear,
a pretty toy for idle hour.
In slothful gardens many a flower
like thee the amorous gods are used
honey-sweet to kiss, and cast then bruised
their fragrance loosing, under feet.
But here we seldom find such sweet
amid our labours long and hard,
from godlike idleness debarred.
And who would not taste the honey-sweet
lying to lips, or crush with feet
the soft cool tissue of pale flowers,
easing like gods the dragging hours?
A! Curse the gods! O hunger dire,
O blinding thirst's unending fire!
One moment shall ye cease, and slake
your sting with morsel I here take!'
Line 4014-4043, from HoME 3: The Lays of Beleriand
He ends this speech by reaching for her; she evades and goes about singing everyone to sleep.
And then in the 'Myths Transformed' later writings (HoME X), Melkor proposes to Arien early on that she be his wife, and when she refuses him, he takes her anyway.
But Melkor, as hath been told, lusted after all light, desiring it jealously for his own. Moreover he soon perceived that in As (the Sun) there was a light that had been concealed from him, and which had a power of which he had not thought. Therefore, afire at once with desire and anger, he went to As and he spoke to Árië (Arien), saying: 'I have chosen thee, and thou shalt be my spouse, even as Varda is to Manwë, and together we shall wield all splendour and mastery. Then the kingship of Arda shall be mine in deed as in right, and thou shalt be the partner of my glory.'
[She says no.]
Melkor did not heed her warning, but cried in his wrath: 'The gift which is withheld I will take!' and he ravished Árië, desiring both to abase her and to take into himself her powers. Then the spirit of Árië went up like a flame of anguish and wrath, and departed for ever from Arda; and the Sun was bereft of the Light of Varda, and was stained by the assault of Melkor.
I bring this up not to suggest that what the Silmarillion needs more of is brutal rape scenes, but rather to make the point that Tolkien himself did employ the broad term of lust to the evil inclinations of his antagonists, and did not exclude the sexual component at times. That doesn't mean we need to come up with scenes showing lust as a particularly sexual appetite, but I don't want our reason for avoiding that to be 'Tolkien would never go there!' because....yes, yes he did.