Your prevailing thought seems to run against the current...:)
A lot of people just really don’t like people that disagree with them on certain issues. I kinda see all of us as “disobedient children on the playground”.
I don’t see it becoming a horrible debacle, North Korea itself is a horrible debacle so if it stays the way it is now, just a waste of time perhaps? If there is any gain from this meeting, it will improve the regional security situation and even a small change would be a win for Trump.
Bottom line is, nobody expects miracles here, but the only thing that would really improve the situation would be unification under the South Korean form of government on the German model. That might be pretty risky for South Korea but it would bring North Koreans into the modern world (only their elites currently have much of a life now) and China would lose nothing really since South Korea has been a placid neighbour ever since the Korean War ended.