Do you think that strongly believing in something makes it right, or pardonable[,] if it proved to be terribly wrong?
Of course it doesn't. Neither does Tony Blair think anything to the contrary, which is why he offered reasons yesterday in support of the decision to go to war. Macintyre ought to know, as well, that 'proved to be terribly wrong' is not like 'weighs more than 400 pounds' or 'stands before us on a platform of solid gold'. People can disagree with one another about certain issues in the light of principles they hold in common and conscientiously but give different weight to, or see differently in the light of the given circumstances. Even changing his or her mind, someone can think that their reasons for the view they originally took were plausible in the light of the evidence available to them at the time. Complexity.