There's the assumption being made by the national security advisers to the Obama administration that the North Korean leadership is not suicidal, that they know they will be obliterated if they attacked the United States. But I would point that everything in South Korea and Japan is well within range of what they might want to do.
We've been in the nation-building business since World War I, and especially since WWII. The goal is not a Jeffersonian Democracy in Afghanistan, but a representative government that respects human rights, protects its own people, and is a friend of the West. These are very realistic - and necessary - goals.