Hm. I think everyone (even crazy dictators) are aware of the effects of nuclear bombing. Knowing that íf you are going to use them you will also can expect some against you will stop everyone from using them I think; even crazy dictators do not want their land to be demolished. I think this reason is the only advantage of multiple countries owning such bombs and weapons.
Honestly, I believe that the only reason why the Americans hasn't invaded Iran or the DPRK may be their fear that these countries might be already possessing the nukes (and powerful enough missiles to launch a nuclear attack with them). Why has the United States invaded Iraq and Libya without valid reasons, while they have held back on attacking Iran and North Korea?