As I alluded to, in reference to your more fully developed argument, the confusing/clarifying point is I think, the question, is there a global system, however unarticulated, that survives the scutiny of competing points of view, of policing norms? Does the US have an exceptional status in this system that the US accepts/craves that is outside the too imperfect normative structure of the UN? If it existed, does it still function well enough or is it broken? Is the Syria crisis in fact a crisis of the system, assuming it exists at all?
These questions seem mostly absent from the discussion except in the occasional "Do we reaqlly want to be the policeman of the world?" which maybe says it well enough if "Does the world want us to be?" is added.
Or something. At first, after the news of the gassing, I formulated various positions for myself. In each case, I would then see or read someone taking that position. At that point my reaction to each was, "Well when you hear it out loud it sounds kinda stupid." Now, mostly what I see is reverse reasoning from one's ideological position.