I'm no Fan of North Korea but if you look at the record -

Used Nuclear Weapons in War time. USA - Yes. North Korea - No.

Used Preemptive Strikes USA - Yes. North Korea - No.

Removed leaders that were Hostile USA - Yes. North Korea - No.

Broken Terms of the Ceasefire USA - Yes. North Korea - No.

Paragraph 13(d) of the Armistice Agreement mandated that neither side introduce new weapons into Korea, other than piece-for-piece replacement of equipment. In September 1956 the U.S. Chairman of the Joint Chiefs of Staff Admiral Radford indicated that the U.S. military intention was to introduce atomic weapons into Korea, which was agreed to by the U.S. National Security Council and President Eisenhower. However paragraph 13(d) prevented the introduction of nuclear weapons and missiles.[34] The U.S. unilaterally abrogated paragraph 13(d), breaking the Armistice Agreement, despite concerns by United Nations allies.

In terms of facing enemies that have Nuclear Weapons it is logical for North Korea to posses Nuclear Weapons.