Unless of course the US is talking about another countries with nukes themselves. But you are making a good case for why it is in each country best interest to acquire nuclear weapons. North Korea appears, in your argument, one of the wisest regimes in the world.
I'm pretty sure that when US is vetoing Russia, it does not mean "we will drop nukes on you if you try this, so don't". Because Russian response will be of the sort "Great, try this and enjoy the fireworks over your population centers, we will hate to see the UN gone with the whole of New York".
