[Gird]

I have myself thought long and hard about this subject, and I think it would work. If they had taken the eagles from the start, then the ring wraiths would still be riding horses, there would be no way to attack the eagles. Also, if they flew above the clouds for the last few miles, they would not be visible to Mordor's armies.

The time would also be lessened so much that Frodo would not be nearly as attached to the ring and would have a lot less trouble disposing of it in the end. He would then not have to go to the grey havens at the end because he'd be perfectly healthy and would feel rest in the shire.

In the worst case scenario, Sauron would sense the ring coming and would have troops all around the mountain. Those troops would be easy enough for Gandalf to take care of and make a path for Frodo to get the ring in. Sadly, Frodo and Gandalf might be sacrificed in this desperate run, but it would be better to lose two then to lose the hundreds and thousands that do die in the story as it is right now.