Why weren't Elrond and Gandalf receptive to letting the ring stay in Rivendell? My claim is that Western military forces could repel the forces of Mordor and Isengard. The invasion would be like Hitler invading Russia - expensive, lengthy.
- Gandalf, Elrond, and Galadriel have the three Elven rings. Nenya in particular would make a land invasion incredibly expensive for Sauron, similar to the Russian winter for Napoleon or Hitler. Elrond could use Vilya to predict the enemy army's movement and Gandalf could use Narya to erect awesome defenses and mount devastating counteroffensives.
- Elven forces are still formidable, with warriors like Glorfindel and Haldir. Theoretically Elrond's envoy to Helm's Deep proves they still have a standing army.
- Thranduil and Galadriel could easily have gotten onboard with erecting defenses, striking against Sauron's army, etc. Gandalf and Aragorn could still save Theoden and get Rohan on board.
The main counterpoints I see are that 1) Sauron's army could move West quickly and easily, through the Gap of Rohan without resistance from Galadriel or Theoden. 2) Elven leaders are not receptive to waging war since they're leaving Middle-earth for Valinor en masse.
But these aren't convincing to me. Ostensibly at this point the plan is to send the Fellowship to Mordor (only a fool's hope). I don't understand why forcing Sauron to project power into the heart of Elvendom isn't a much safer bet.