Kill thousands of human beings because of one incredibly roostery leader?
Sure.
But it's because their leader is a danger to hundreds of millions abroad and a nightmarish reality to 25 million at home.
He executes people with anti aircraft guns, assassinates people internationally (even family), and starves his citizens while publicly executing those who do anything deemed remotely wrong.
He is a threat to everyone outside north korea. If a nuke made it undetected to Japan, S. Korea, or Hawaii, etc. Millions would die.
Killing a few thousand N. Korean government and military men is a small price to pay for eliminating such a danger.