All in all, it was an object lesson in the dangers of groupthink, a demonstration of how important it is to listen to skeptical voices and separate reporting from advocacy. But as I said, it’s a lesson that doesn’t seem to have been learned. Consider, as evidence, the deficit obsession that has dominated our political scene for the past three years.

Now, I don’t want to push the analogy too far. Bad economic policy isn’t the moral equivalent of a war fought on false pretenses, and while the predictions of deficit scolds have been wrong time and again, there hasn’t been any development either as decisive or as shocking as the complete failure to find weapons of mass destruction. Best of all, these days dissenters don’t operate in the atmosphere of menace, the sense that raising doubts could have devastating personal and career consequences, that was so pervasive in 2002 and 2003. (Remember the hate campaign against the Dixie Chicks?)

But now as then we have the illusion of consensus, an illusion based on a process in which anyone questioning the preferred narrative is immediately marginalized, no matter how strong his or her credentials. And now as then the press often seems to have taken sides. It has been especially striking how often questionable assertions are reported as fact. How many times, for example, have you seen news articles simply asserting that the United States has a “debt crisis,” even though many economists would argue that it faces no such thing?

In fact, in some ways the line between news and opinion has been even more blurred on fiscal issues than it was in the march to war. As The Post’s Ezra Klein noted last month, it seems that “the rules of reportorial neutrality don’t apply when it comes to the deficit.”

What we should have learned from the Iraq debacle was that you should always be skeptical and that you should never rely on supposed authority. If you hear that “everyone” supports a policy, whether it’s a war of choice or fiscal austerity, you should ask whether “everyone” has been defined to exclude anyone expressing a different opinion. And policy arguments should be evaluated on the merits, not by who expresses them; remember when Colin Powell assured us about those Iraqi W.M.D.’s?

Unfortunately, as I said, we don’t seem to have learned those lessons. Will we ever?