What plausible purpose do these weapons serve (except deterrence itself), fully knowing that using them will almost guarantee massive retaliation?
Even if we do manage full denuclearization, it'd be pretty darn hard to keep it that way seeing as how we can't even stop North Korea from joining the club.
NK joined an exclusive club and now Kim is rewarded with a visit from Trump. In this version of the world, possessing nuclear weapons is a source of legitimacy for any country. In a non-nuclear world, actions to obtain them will prompt imediate preemptive conventional attacks. Russia, US and EU could agree to maintain minimal deterrence capability against rouge actors like NK, but insufficient for global war.
There are plenty of ways to sufficiently deter a preemptive conventional invasion and North Korea is a perfect example of it. Their conventional artillery poses a significant threat to Seoul, which by itself put a huge damper on any talks about conventional warfare to topple the regime or attack their nuclear facilities.
> You can't build a nuclear arsenal overnight.
True but it's extremely hard to verify that the other party isn't hiding a 100-200 warheads in some remote barely documented base and hid the extra production in lost/modified paperwork. Larger countries with larger militaries just make the number of possible hiding spaces that much higher.
This seems an implausible strategy on the long run, to organize such a conspiracy you would need thousands of people in the know, from political leaders to technicians. The value of this intelligence would be so colossal that it's unfathomable nobody would sell it for profit or release it for conscience reasons. See the Israel story and Mordechai Vanunu.
Then again, if you manage to have a stockpile of nuclear pits (actual warheads require continuous maintenance, Tritium replenishment etc.) that only 15 people know about, in an non-deployable configuration and hide them so deep that the ultra-sensitive nuclear detectors mandated by the treaties can't sense them, is that a major threat? Their existence might simply fade out of institutional memory.
I think this has been the case with NATO, Israel, Saudi Arabia, Korea, Taiwan, and Pakistan.
On the balance, this obviously doesn’t make the overall strategy sound in the long-run, but the nuclear enterprise has been myopic from the beginning.