Some of those issues reflect inertia and misplaced trust.  Both Truman and the UN wanted to reunite Korea per pre-war UN declarations.  But only if the Chinese wouldn't intervene.  Given MacArthur's renewed prestige due to the success of the Inchon Landings, which no one but him thought would work, his assessment that the Chinese wouldn't intervene wasn't questioned.  He would deny that he could have made such an assessment in testimony before the Congressional committee investigating the conduct of the war.  But as I said in a paper I presented many years ago, MacArthur was all too eager to play the expert on the Oriental mind.