An antagonist with redemptive qualities make for a better story.

Think Gollum vs Sauron.
A story cannot be written about pure evil but around it otherwise human conscious observers would not be able to relate to the antagonists drive to do the obviously wrong and self serving thing.

Mankind and their lust for power and illusions of grandeur is a bigger threat to Middle earth.  Elves are indifferent and reactionary. Dwarves are greedy. Hobbits are small.  These are the more interesting "antagonistic forces" which allows the story to have progression and scope in it's urgency.