This is like saying no to having an infected appendix removed because it will hurt.
This is all well and good if you're willing to kill hundreds of thousands of South Koreans and possibly subject Japan to nuclear fallout on the unproven assumption that NK has nuclear missiles ready to go.
If you happened to be vacationing in Seoul with family and friends, would you be so ready to sacrifice your life and theirs on that assumption?
It's easy to be brave when you have nothing to lose.