The goal is to prevent NOKO from obtaining a reliable and accurate nuclear missile arsenal.  He will use that to blackmail and threaten other sin the region.  And yes, China would use him as a proxy to further their goals in the region.  Eventually the viable threats would extend to the US.  And Kim would export he missile and know-how to other bad actors like Iran.  There is no good or painless solution answer here but something has to be done.