A decade after 9/11, Americans for the most part seem to have settled down and accepted the straightforward, monstrous reality of what happened. But the journey was a close call. Just a few years ago, many had nearly lost their grip. More than a third of the public embraced a cuckooland version of the terrorist attacks that suggested the onset of national psychosis.

At the height of the lunacy in 2006, 36 percent of respondents to a Scripps Howard/Ohio University poll said it was probable that the 9/11 attacks on the World Trade Center and Pentagon were an “inside job,” and that U.S. officials either assisted in the planning and execution or did nothing to stop them. A Zogby poll in 2007 found similar sentiment.

No doubt some Americans only flirted with this idea of an unprecedented scale of treachery in the upper reaches of government. But many embraced conspiracy with a scary gusto, as I found out when I wrote columns praising the 2006 book “Debunking 9/11 Myths: Why Conspiracy Theories Can’t Stand Up to the Facts” by writers and researchers at Popular Mechanics.

The irate response equaled anything I’ve experienced in decades of journalism, and my e-mail box was clogged for days. Some readers patiently attempted to expose my ignorance of the intricacies of the grand conspiracy, but most denounced my transgression in the most extravagant terms. I was a coward, traitor, accessory to the crime, contributor to the cover-up, shill for the corporate media, fascist, patsy for Israel, and much more.

What accounted for this loss of mooring, this epidemic of delusion? To some extent, of course, it reflected dismay over the military fiasco in Iraq, the administration’s false claims about weapons of mass destruction, and raw hatred for George W. Bush.

Even so, high-running passions are no excuse for believing in theories such as the controlled demolition of the Twin Towers and World Trade Center Building 7 that are highly improbable on their face. And political anger is no reason to discount the evidence of thousands of eyewitnesses, let alone the detailed explanations of a multitude of experts at venues such as the National Institute of Standards and Technology.

To the contrary, the widespread embrace of 9/11 conspiracies is a sorry reflection on the gullibility of the public and its willingness to believe just about anything if it serves a larger agenda. If our leaders are performing badly, it can’t merely be because they’re incompetent or misguided. They must be evil as well. They must be willing to slaughter thousands of their fellow citizens in a spectacularly complex operation in order to justify an imperial scheme for Afghanistan and Iraq (the spoils of Afghanistan being mysteriously irresistible, it seems).

In recent days, the online publication Slate has run the best series of articles I’ve seen on the origins, growth and partial decay of the 9/11 conspiracy movement. But as writer Jeremy Stahl explains, the movement still boasts teeth. When conspiracy activist Charlie Veitch renounced his beliefs earlier this year, for example, he was “immediately flooded with hate mail and death threats.”

Meanwhile, an Angus Reid Public Opinion survey has found 14 percent of respondents still consider the collapse of Twin Towers “the result of a controlled demolition,” while 16 percent agree that United Airlines Flight 93 was shot down.

Those percentages may not come close to what they would have been five years ago, but they’re still a disgrace.

E-mail Vincent Carroll at vcarroll@denverpost.com