It amazes me how you are always able to come up with so many quotes in such a short time.
But if Melkor had no chance but to fall to evil, we cannot hold him responsible for it, at least not by the standards of justice that we nowadays apply. His punishment was unjustified and even though he had some good times, I would agree that his story is the saddest of all.
The question that arises is 'Whom do we hold responsible for evil, now?'. (I just realized that it maybe just shows how pitiful humans are that they always have to blame somebody for what they call 'evil') If we want to blame somebody, we are left with no other candidate than Eru himself. Eru of course would not be evil, he would combine both good and evil in himself.
Somewhere (there you have it
), I think, is written, that evil in Eä is defined as a revolt against the will of Eru. How can this work if evil
was in the will of Eru?