Something needs to be done but NK is basically holding Japan and SK hostage(now Guam as well). Hundreds of thousands if not millions would die including many Americans stationed overseas.
The question to be asked, and it's a big one, is what does the future hold? Doing nothing could be just a less serious second Cold War. On the other hand, a war could be inevitable. Do you risk 1-2 million lives in a pre-emptive attack and shorter war or wait until everybody's at their strongest and have a meat-grinder that ultimately results in way more death all-around and takes longer to resolve? If France and Britain had called Hitler's bluff with the remilitarization of the Rhineland, WWII would've probably just been Europe building a wall to keep Stalin out (with or without toppling the Nazi regime, depending how the confrontation went) and the Japanese being forced to chill the fuck out by a united west they couldn't hope to fight.
I'm still not sure how an invasion would help matters, given the size of their army ---