I agree with your article in general, but this specific point is wrong. You seem to imply that it’s never appropriate to threaten countries. Replace the word “North Korea” with “Nazi Germany” and you’ll understand why sometimes this kind of behavior is very much appropriate.
There is a time and a place to use force, or even forceful language, against countries who repeatedly threaten to wipe out their neighbors. How do you think the people of South Korea feel? They’ve been negotiating with North Korea for years and where has it gotten them? Their bullying neighbor decided to threaten them with nuclear weapons.