1. Are you willing to gamble that any nuclear weapons are nonfunctional? That seems like a bridge too far.

2. How do you know the US nuclear arsenal is not equally defunct? Nuclear arsenals are notoriously secretive.

3. You don't need 5000 nukes to destroy the world. You don't need 500 nukes. You could knock your enemy off the board with 50. Or 25. Or 10. Or 2. You don't need many nukes to kill a lot of people.