morgoth

[Nils]

Why did Ilúvatar not just destroy him or call him back from earth?

The Music had to become reality. The Music was tainted by Morgoth, so Ea too had to be marred.

Would be easy for him to do it right? It would have saved the people of Ëa a lot of trouble.

This is what the Silmarillion says about the third theme:

Then again Iluvatar arose, and the Ainur perceived that his countenance was stern; and he lifted up his right hand and behold! A third theme grew amid the confusion, and it was unlike the others. For it seemed at first soft and sweet, a mere rippling of gentle sounds in delicate melodies; but it could not be quenched and it took to itself power and profundity. And it seemed at last that there were two musics progressing at one time before the seat of Iluvatar, and they were utterly at variance. The one was deep and wide and beautiful, but slow and blended with an immeasurable sorrow from which its beauty chiefly came. The other had now achieved a unity of its own; but it was loud, and vain, and endlessly repeated; and it had little harmony but rather a clamorous union as of many trumpets braying upon a few notes. And it essayed to drown the other music by the violence of its voice, but it seemed that its most triumphant notes were taken by the other and woven into its own solemn pattern.

The result was a marred creation. Evil did exist, but it helped to create something more beautiful.


I believe a comment made by Mandos to Manwe also answers the question about why evil was allowed

'Dear-bought those songs shall be accounted, and yet shall be well-bought. For the price could be no other. Thus even as Eru spoke to us shall beauty not before conceived be brought into Ea, and evil yet be good to have been.' But Mandos said, 'And yet remain evil. To me shall Feanor come soon.'