Although I can understand those who appear to be in favour of NK having nuclear weapons as a means of defence but bear in mind (edit):
1. This strong defence keeps a rather nasty regime in place
2. This regime needs hard currency to survive (starving the population only gets you so much), how much can they generate through selling both this weapon and rocket technology?
And for all those saying that China will do something about this, they will not. The existence of NK is an irritant to South Korea (a major trading rival), Japan (an historical adversary) and America (an ideological enemy) without affecting their business with all 3 nations plus if South and North Korea did peacefully merge then chances are American bases would be even closer to their border.
And as for us having nuclear weapons I thought that was explained years ago, its because the French have :)