Have ye then no hope?

[HerenIstarion]

"Well there's no point in opposing the Dark Lord. He won't win in the end."

That's why, I believe, Tolkien hints at Evil as outside force too, not to let such paradoxes arise, for one thing.

On the other hand, if to be Good means to follow some inherent standard put there by Eru, than such an idea on behalf of an elf would be dereliction of duty, i.e. becoming Evil oneself.

theoretical possibility that they will, en masse, either avoid that responsibility or fail in their efforts to uphold it, in which case "Good" will not prevail

And for such cases there is direct intervention, if I may be so bold as to utter the word, reserved. Numenor, per instance.