"In any case, those who believe in "international law,"... constantly make this case - that aggressors can be deterred by good guys forming clubs and signing treaties. If it's really true that collective security agreements do not alter the behavior of potential aggressors, and that nations participating in multilateral security agreements will not honor their obligations, then multilateralism is moot and they should stop preaching it."

Good guys is too easy... the point of multilateralism as i see it is to engage multiple countries in finding the common interest (ie avoid conflict) and using that as a starting point for negotiations - this is kaplans point about 'where are the summits'. Multilateralism can break down, of course, especially if there are too many voices at the table clamoring for their own interests... rationally we have to figure out who has leverage, who can aid us in this discussion, and mobilize all avenues of diplomacy (ie talking to the enemy of today's parlance) to create these discussions.... unilateralism, as you acknowledge, is an abject failure. any other option must be explored.