As a rule of thumb, I don't want more autocracies to have access to nuclear weapons.
It depends on your definition of autocracy. The United States president doesn't need the permission of Congress to use a nuclear weapon. So the president can act at will, that doesn't look democratic.
They have proven themselves incapable of attacking and overthrowing a regime which has access to nuclear weapons, because of the military doctrine of mutual nuclear destruction.
I might be wrong, but some of the nations the US claimed have nuclear weapons turned out to be fake. Iraq is an example.
North Korea is a small insignificant country with little resources and still the USA does not dare to mess with them because those nukes, it is what the regime of Tehran wants to accomplish and what the United States seeks to prevent at all cost, because Iran sure is not as small and insignicant as NK is. It has vast resources and are capable of actually becoming a threat to western values.
Negotiations would have been the best option. Libya peacefully gave up its nuclear programmes through dialogue and not by force.