Of course you wouldn't ignore a dud. The question is do you attack a country because they develop nuclear weapons and ICBM's because they don't like you? When you can't predict the full consequences of an attack, or for that matter can't establish a reasoning for that country to want to commit collective suicide?
The reply to this is rather easy. Would you rather live with the deaths of 3 million innocents or criminals?
How do you know it would be 3 million death? A nuke on Japan would be considerably more.N-Korea is over 25 million people. S-Korea is 50 million. If the US carries out an unprovoked attack, how would China respond? Or the rest of the world for that matter. There are so many variables in this equation it should make your head spin. Not to mention that you still haven't established a real reasoning why a country with 25 million people would attack a country of 50 million backed by the most powerful nation in the world. Why do you feel the US is justified risking the lives of more then a hundred million people and if this escalates possibly the world on the assumption the leader of S-Korea is suicidal?
The instant kill zone of the nuke dropped in Japan was 1.6 square miles. I just looked it up.
So, lets assume that N-Korea would only kill a million Japanese. 25 Million N-Koreans would likely die in retaliation. All because the US assumed that N-Korea was irrational enough to commit suicide. Do you know how that scenario ultimately pans out? Show me an actual reasoning behind your belief that N-Korea would start something and then you might have a point.
Here's my reasoning:
1. NoKo sells arms to the highest bidder. They're no reason to believe they would not sell nukes to terrorists.
2. NoKo is determined to united all of Korea. They're ability to nuke Japan and the U.S. gives them the leverage to force the U.S. out of Korea and SoKo into submission.
3. NoKo can use the threat of nukes to get anything they want as long as the U.S. does not take action.
4. If the U.S. is forced to take action in the future, after NoKo has a full nuclear arsenal, the consequences will be far worse than if the U.S. takes action now.