The flip side of your argument is it accepts the Kims' ownership over North Korea's land and population. The concept of legitimacy is fuzzy. There is gray area between defense and colonialist conquest.
It's implicit in your statement that the moral repugnancy of the Kim regime makes any acceptance of its existence intolerable. But that clearly implies we should remove the Kim regime; but invading countries is also generally immoral and the consequences of Korean War II are also morally repugnant.
> that clearly implies we should remove the Kim regime
No, it just means we can discuss it without moral censure. There have been lots of multilateral and unilateral interventions, covert and overt, since World War II. Global stability is built on great powers not warring with each other.