How could Turin return?

[Dimaldaeon]

Heres my attempt at trying to explain why the Valar didn't kill Morgoth.
Evil can never really be killed. There must always be a balance in the world. I mean if there is no evil how will we know what is good, if ther were no shadows how would we know what is light. Tolkien also used his religious beliefs to great extent in the Sil. In the Bible, the final chapter to be exact, it states the God will not kill Satan in the conventional sense, yes he and the Dragon and the False Prophet will be cast into the lake of fire but it dosen't state the God will unmake him. Speaking of religion, Tolkien also greatly believed in forgiveness and redemption. He states the nothing was evil in the beginning and nothing is completely evil. Evil is not in itself a single entity it is a byproduct of pride and jealousy