North Korea You've misread the situation. Considering the state of Western media, most people do.
You know Iraq wasn't invaded because of human rights, that was merely emotional rhetoric to stir up support for the war. The real reason for the invasion was a neoconservative belief that democracies are more likely to do business with other democracies; converting a "pillar" of the Middle East into a democracy was supposed to have a "domino" effect, meaning other autocracies would follow their lead. This, in turn, would burgeon commercial enterprise between the US, the UK and other recently-turned democratic Middle Eastern states. People talk about the petrodollar, they talk about the weapons of mass destruction, they talk about the welfare of Iraqi citizens under Saddam Hussein - none of that had anything to do with it. Mostly it had to do with what I just outlined, as well as allowing the West to counter Iranian domination in the area (and, by extension, Russian interference). The great game.
Onto North Korea. Consider Iraq. Consider Libya. Iraq was invaded because the US knew it didn't possess nuclear weapons and thus mutually assured destruction was not a viable option. Libya, on the other hand, possessed a nuclear article. Gaddafi was only overthrown after he naively agreed to give up his nuclear arsenal following extended diplomatic discussions with the West. North Korea has no intention of ever using its nuclear weapons. Ever. There is no nuclear threat from North Korea to anyone in the world, despite the madman scenario Western media depicts. Truth of the matter is that North Korea has sustained itself for eighty years by being a calculated and rational player in foreign relations. It knows that the only way it can ensure it won't be invaded by other countries is to continue bolstering its nuclear supply and throw out a few crazy threats every few months to keep everyone on their toes. The country is topical now because there's a lot of uncertainty around the South China Sea, with South Korea possibly looking to do more business with China than the US, and China, naturally, being the world's next superpower, is North Korea's only true ally (and even then that relationship is frayed). It's a question of geographical dominance. North Korea is merely a proxy. Their nuclear weapons and capability of wiping out Soeul are just guarantors of their prolonged security. Add onto that the fact that China and South Korea (and Japan, how did I forget Japan) will never let the US try anything without massive retaliation, you realise the situation is the product of military flexing and posturing. Nation states only care about their own survival - there is far too much risk to invade North Korea in order to save its citizens, but even if there was mitigated or minimal risk, no country would do it because there's nothing to gain from doing so on an economic basis. No war has ever been about liberating a certain people from an oppressive regime, despite the tendency to frame it as such.
Edit: if you think for a second that the US or any other nuclear power are going to give up their nuclear arsenal then you should do some serious reading because all that's going to happen from here on out is nuclear proliferation.
Edit 2: so as for what we should do about North Korea, absolutely nothing. Everything works out better that way for everyone.