[Inziladun]

Looking back on this thread, I note that the subject of the Vala Aulë's error was mentioned, but not explored.
Aulë, of course, "made" the Dwarves (physically, though not in a spiritual sense), something that he knew was beyond his authority. Melkor "made" the Orcs, by perverting existing Children of Ilúvatar already embodied with the One with fea. Melkor too understood the serious illegality of his act. Once again, we begin with different intentions, which in their turn lead to different end results for the offenders.

Aulë acted out of mere impatience; he wanted to teach his knowledge and instruct others in the building of Arda, and the glorification of the One thereby. As soon as Ilúvatar spoke to him about the matter, he was filled with shame and true remorse. That fact was recognized by Ilúvatar, who reacted by forgiving Aulë and giving the Dwarves a part in the Music.

Melkor, on the other hand, never was truly repentant for anything he did. Like the career criminal who says "I'm sorry" to the judge about to levy a heavy sentence, Melkor was only frustrated that he'd been caught. After his offense regarding the Orcs, he was put in prison. There can be no doubt he knew full well the nature of his crimes. Yet, he thought all the time only of how to perfect his technique so as never to be brought to justice again. His ultimate fate was to be cast into the Void.

So, we have one Vala gaining understanding of his misdeed and correcting his behavior, and thus is given a "slap on the wrist" by the Judge. The other is seen to be hardcore to the end, and gets what amounts to e life sentence. To me, intentions seem to be the key to redemption.