It was by no means “all” the “Smart People”, even back then. The recovering Iraq War hawks of today (as opposed to all the Iraq War hawks still in denial, of whom there are also plenty) try to shift the blame for their reckless opportunism onto some kind of zeitgeist-hivemind situation that just sort of hypnotized otherwise rational people into unanimous war fever. “Sleepwalking”, if you will.
But the war fever was very far from unanimous, and its chief proponents were not “otherwise rational” in any reliable sense. They were cheerleaders for US imperialism, and they saw what they thought was an irresistible opportunity. They, including the many recovering Iraq War hawks at the New York Times, can’t duck that responsibility now by pretending that golly gee folks, we were all just sort of in a trance. There is plenty of documentation of deep non-unanimity on that issue at the time, including here on these boards.