[Sharkû]

Very clearly, the origin of all evil in Eä lies in Melkor, precisely in his discords in the Music:

"In this Myth the rebellion of created free-will precedes creation of the World (Eä); and Eä has in it, subcreatively introduced, evil, rebellions, discordant elements of its own nature already when the Let it Be was spoken. The Fall or corruption, therefore, of all things in it and all inhabitants of it, was a possibility if not inevitable." (Letter 212)

As can be seen, he is not only the originator of evil in Eä, but also the very embodiment and incarnation of Sin: "Melkor had abandoned for ever all 'spiritual' ambitions, and existed almost solely as a desire to possess and dominate matter, and Arda in particular." (MT)

This ab-original evil is, in turn, the very sin of Pride; per Later QS, Laws A [= HoME X, 3, II, iii]: ""trust in Eru the Lord everlasting, that he is good, and that his works shall all end in good. This the Marrer hath denied, and in this denial is the root of all evil, and its end is in despair" (emphasis mine).

With that cf. Summa Theologiae: ""inordinate self-love is the cause of every sin (1,77) ... the root of pride is found to consist in man not being, in some way, subject to God and His rule."

It is therefore clear that Pride may not on all occasions be the origin of Sin, or the reason behind committed evil; but it is very much the first and greatest sin on a cosmogonical level – Melkor's pride led to him introducing new themes of his own, thereby introducing evil in Eä.
Pride in Middle-earth usually does not reach that far, it is generally unknowing rejection of Eru's will; sometimes, that is, in later ages, simply because many people do not know Eru or his will at all.

Those more in the know, sc. the Quendi, are different: "but not one [Elf] had ever entered the service or allegiance of Melkor himself, nor ever denied the existence and absolute supremacy of Eru. Some dreadful things of this sort, Finrod guesses, Men must have done, as a whole;" (HoME X, 4 [Athrabeth commentary])

Now arises the question to what degree we can counterpose Sin, especially as explained above, to Virtues. I would hesitate to go beyond what Finrod explained:

"'Have ye then no hope?' said Finrod.
'What is hope?' she said. 'An expectation of good, which though uncertain has some foundation in what is known? Then we have none.'
'That is one thing that Men call "hope",' said Finrod. 'Amdir we call it, "looking up". But there is another which is founded deeper. Estel we call it, that is "trust". It is not defeated by the ways of the world, for it does not come from experience, but from our nature and first being. If we are indeed the Eruhin, the Children of the One, then He will not suffer Himself to be deprived of His own, not by any Enemy, not even by ourselves.
This is the last foundation of Estel, which we keep even when we contemplate the End: of all His designs the issue must be for His Children's joy. Amdir you have not, you say. Does no Estel at all abide?' " (HoME X, 4)