It's probably the case that North Korea is near the top of the list of Worst Places on the Planet. And, I'm all for regime change there. However, there's a wee little problem. The first is that North Korea is indeed a threat to its neighbors, with conventional and we believe nuclear weapons. The second is that our conventional military is pretty tied up at the moment. The third is that even if we did go all nuclear on NK (and don't think there aren't people in the administration who think we must nuke the village in order to save it) that probably wouldn't make Japan, China, or South Korea particularly happy or healthy. The fourth is that Dear Leader is nuts and in a game of chicken he isn't going to blink.
But, all that isn't going to stop all the nutcases in power from pushing us to war...