Because the regime has always been crazy, even as it passes through different rulers. The best case scenario of North Korea is that the world is faced with a humanitarian crises on a shocking scale that will cost tens of billions of dollars to correct. The expected lower limit of the results of foreign action working to take down the North Korean regime would be the deaths of hundreds of thousands or millions of South Korean civilians (in a matter of hours) due to shelling from thousands of DPRK artillery positions. The possible upper limit of badness would be the North Koreans hitting Los Angeles, San Francisco, Seattle, Taipei, Tokyo, and Seoul with nuclear and/or chemical weapons on ICBMs, IRBMs, aircraft, or smuggled onto commercial cargo ships.
