Because nukes are intended for a crushing reprisal within minutes of an attack, before the attack can wipe out all the weapons, just one person in each country gets to decide when to have a nuclear war. They have to make the decision in minutes.
You want this person to be like no-drama Obama. He has to be calm, unflappable, rational, self-doubting.
The last person you want is someone with a mental illness, e.g. paranoia or grandiosity or even someone with a quick-flash temper or prone to jump to conclusions.
It is thus important to get crazy people such as Kim Jong-un or Donald J. Trump out of such positions. It is morally justified to use any conceivable means to oust them. Ignoring the danger condemns the earth to flames and the extinction of most species.~ Roedy (1948-02-04 age:70)