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Quite so, Baz.
My main worry is that the existing nuclear powers understand their use as a deterrent*. I'm not sure that NKs share that outlook or whether they would unilaterally hit out at their (perceived) imperialist threat (ie "the West") and, if they did, then what? Each attempt, by us, to retaliate becomes the justification for the next one off their production line. It would be like the Israel/Palestine situation.
But if we fail to retaliate, we're doomed to be pushed around by their demands forever.
* against land invasion. Only two countries can do this without a long - and conspicuous - sea voyage. Where's the threat, against them?