If you think China, South Korea, and Japan want Trump to initiate hostilities with NK, you're NUTS. They are all urging diplomacy and restraint. Moon opting for missile defense, is just that, DEFENSE. He's not anxious for a war that might kill millions of his countrymen.

With Iran we opted for negotiation instead of military action. A lot of people called that appeasement too. So far it appears to be working, although Trump is reportedly eager to scuttle the agreement.
It would be great if we could negotiate some kind of face saving agreement with NK, but short of that, we will simply have to accept them having nuclear missiles. Then our only options are containment, sanctions, and developing an effective missile defense. 

War is unthinkable. If you thought Iraq was a disaster, just wait for the Second Korean War.