3.  The Israelis helped to mitigate the risk posed by Hussein by bombing his nuclear reactor.  Still, Hussein paid suicide bombers' families $25K and regularly aided terrorists who killed Israelis.

4.  Hussein was a psychopath without nukes and ICBMs.

5.  Many see the DPRK as China's useful pit bull.  If China wished to stop Kim they could cut off his oil supplies and access to banking.  Kim deflects US attention away from China's theft of land on the Asian sub-continent and the South China Sea as well as key trade and currency manipulation issues.

Chinese troops on the border may well be there to support Kim, as was the case in 1950, if the US & SK attack NK.

Russia also supported the Kim dynasty during the Korean War.  They are much more likely to pounce on Allied troops than they are on Kim.

6.  Your skepticism is understandable, but Kim, unlike Hussein, poses a real threat to the US, as demonstrated by his ICBM test yesterday and his nuclear tests.

Better safe than sorry.