The assertive "broken record" technique Jgnat demonstrated above can be very effective.
You don't argue the manipulative with person's premise.
You agree hypothetically but stick to your position.
Elder: "Armageddon is coming any day. If you resign now, Jehovah might not consider you worthy to survive."
You: "That would certainly be tragic, but I've decided to resign."
Elder: "But why would you do such a thing?"
You: "I appreciate your concern, but I've decided to resign."