[Raynor]

Originally Posted by Macalaure

Melkor didn't have to fall to evil, he could have chosen otherwise.

I disagree:

Originally Posted by Manuscript A, Of the severance of marriage, Later Quenta Silmarillion, HoME X

For Eru is Lord of All, and moveth all the devices of his creatures, even the malice of the Marrer, in his final purposes, but he doth not of his prime motion impose grief upon them.

Originally Posted by Letter #200

Sauron had been attached to the greatest, Melkor, who ultimately became the inevitable Rebel and self-worshipper of mythologies that begin with a transcendent unique Creator.

Originally Posted by Letter #153

Free Will is derivative, and is.'. only operative within provided circumstances; but in order that it may exist, it is necessary that the Author should guarantee it, whatever betides : sc. when it is 'against His Will', as we say, at any rate as it appears on a finite view.

Originally Posted by Note 7, Atrabeth Finrod ah Andreth, HoME X

[Eru] must as Author always remain 'outside' the Drama, even though that Drama depends on His design and His will for its beginning and continuance, in every detail and moment.

I believe that the conclusion, in the light of these arguments, is that Eru meant for Melkor to 'fall'; all in all, I don't think Melkor had that a bad ride , well, unless we count his temporary end on Arda.