Earlier quoted context omitted.
I'm not at all confident in the ability of the US to "clean up this mess". Similar arguments were made before the war in Iraq. I won't defend Saddam but I don't think you can argue that the average Iraqi ended up better off.
Stalin and Mao supplied Kim Il Sung in the Korean War because they didn't want democracy to spread to Asia. China and Russia are still obstructing the US with the same goal of preventing democracy. If we don't do it no one will. The Kims have proven their ability to retain power. Some people think death is better than having to live in North Korea: http://www.worldtribune.com/senior-north-korea-official-and-...
-The United States propped up the corrupt and vicious right-wing ruler Syngman Rhee, who was responsible for thousands of extrajudicial killings of his political opponents. And also not a real fan of democracy
-His reign of murder and repression created a context in which, Kim Il Sung, by opposing him, could build on his reputation as an Anti-Japanese occupation guerilla to become a populist hero.
-Who, in the imperial conquest by proxy battle known as the Cold War, then became the Chinese and Soviet’s man in the Korean Peninsula.
So neither side really fighting for or against the spread of democracy. Just their own interests. And everything is still a mess as a result!