People frequently try to refute my pacifism by merely saying "Hitler." "If only Britain and France had declared war and unseated Hitler when he occupied the Rheinland in 1936!" they say. My quick reply is, "Yes, but I've got a better one. If only any of the major powers in World War I had been pacifist in 1914, neither Nazism nor Communism would have gained power in the first place!"
If you think that's an unfair historical counter-factual, I agree. They're both unfair historical counter-factuals. What's unfair about them? Both test political philosophies by picking the exact historical moment when - with 20/20 hindsight - they perform most badly. Using this rhetorical strategy, you can make any philosophy whatsoever look asinine.
So what would a fair use of historical counter-factuals look like? It's hard to say, but here's where I'd start: Imagine what would happen if the philosophy in question were popular - or at least influential - for a century. Alternately, imagine what would happen on average if the philosophy in question were popular.
I think pacifism does well by either of these standards. And even if I'm wrong, I'm not obviously wrong. You can't pretend to refute me merely by invoking the name of Hitler.
Of course, "Fight when it's a good idea, make peace when it's a good idea" counts as a philosophy. And you might think that this case-by-case approach has to yield better results than pacifism. But that's only true with perfect foresight. In the real world of uncertainty, case-by-case optimization is often inferior to simple rules. Which, as I've explained before, is the heart of my case for pacifism.
P.S. If you have any doubts about the uncertain effects of foreign policy, don't miss Gardner and Tetlock in this month's Cato Unbound on "What's Wrong With Expert Predictions?" The intro alone is worth the price of admission:
Each December, The Economist forecasts the coming year in a special issue called The World in Whatever-The-Next-Year-Is. It's avidly read around the world. But then, like most forecasts, it's forgotten.
The editors may regret that short shelf-life some years, but surely not this one. Even now, only halfway through the year, The World in 2011
bears little resemblance to the world in 2011. Of the political turmoil
in the Middle East--the revolutionary movements in Tunisia, Egypt,
Libya, Yemen, Bahrain, and Syria--we find no hint in The Economist's
forecast. Nor do we find a word about the earthquake/tsunami and
consequent disasters in Japan or the spillover effects on the viability
of nuclear power around the world. Or the killing of Osama bin Laden
and the spillover effects for al Qaeda and Pakistani and Afghan
politics. So each of the top three global events of the first half of
2011 were as unforeseen by The Economist as the next great asteroid strike.