I think that countries with an imperialistic or aggressive neighbor should have the nuclear weapon, but this countries should be democracies, otherwise an insane or fanatic dictator/regime can just use it even if it will wipe out his country since he might think they go to heaven and get their rewards there.

I understand that countries that already have their weapon do not want the smaller countries to get it, and a lot of people from big countries are OK if small countries get genocided if it prevent ww3 or if it keeps the bills down.