In a recent essay, at project syndicate, Bioethicist Peter Singer has a thought-provoking piece on Wikileaks' Cablegate, in which he discusses The Treaty of Versailles, one of the most notable pieces of secret diplomacy.
Singer states. "I was reminded of Wilson’s 1918 speech in which he put forward “Fourteen Points” for a just peace to end World War I. The first of those fourteen points reads: “Open covenants of peace must be arrived at, after which there will surely be no private international action or rulings of any kind, but diplomacy shall proceed always frankly and in the public view.”
Since the treaty bore substantial responsibility for several of the conditions that led to World War II, Singer says "it has a fair claim to being the most disastrous peace treaty in human history." He brings up points both pro and con:
Is open diplomacy possible? (project-syndicate.org)