There are over 10,000 fairly high yield nuclear warheads either sitting on missiles, in bombs, or in storage that could each destroy an entire city. Nobody wants to use them. Nobody really wants to see them used.
Only an insane person would ever actually launch one unless one was already headed towards them. The only reason anyone keeps them is because the other guy has them. The only reason we can't agree to dismantle all of ours at the same time is because we don't trust them and they don't trust us not to hide a few "just in case".