I originally posted this in the comments at Crooked Timber as an aside, but thought it deserved elevation of sorts:
It’s worth remembering the very limited harm that was done by Tony Blair’s stupid and wrong decision to get involved in Iraq. The net result was that:
a) a lot of people internationally thought the British were slightly more wankerish than they previously thought us, at least until they forgot about it again.
b) the risk of Islamist terrorism against UK nationals rose from imperceptibly low to still imperceptibly low but slightly higher than before.
Also, some of the military casualties of the war became people with British passports instead of people with American passports, and some of the civilian casualties of the war were shot or bombed by people with British passports instead of people with American passports.
But as far as I can see, that doesn’t affect the total harm done, unless you think the British Army is appreciably worse than the US Army at minimising casualties (which doesn’t appear to be the case either from the casualty data or the anecdotal evidence that I’ve seen), or that American deaths are more acceptable than British ones.