I agree it "should be done" on one hand, but on the other, I'm really not willing to killing 10-15 million people to do so. Are you?
NK has over 50,000 rocket and artillery tubes pointed at Seoul. I've SEEN the war plans, the estimates and all that good stuff. NK's war plans call for pounding Seoul as the opening move. Even if, and this is a big if, the war stays conventional, the casualty rate for the city is est. 50% in the first 30 min of a shooting war. If they use CBR, 70%.
That's why there hasn't been another Korean War. And why attacking NK's nuclear facilities is not really an option.