Had someone suggested in 1972 that the president of the United States personally knew about and authorized secret agents to literally break into his political opponents hotel room in order to find information to be used against him in the coming campaign, most ordinary people would have called them a "conspiracy theorist". But they would have been right. Had some one suggested that the US government sent CIA officials to assassinate the democratically elected rulers of socialist South American countries, or that the administration was making arms trade deals with Iran to fund insurgents in a democratic society, they would be labeled a "conspiracy theorist". But these things happened. There is this stigma attached to the word "conspiracy" as though it belief in one automatically makes them insane or at least without credibility. But the fact remains that conspiracies exist. A conspiracy is just a group of people getting together to discuss the details of a crime. The rich and powerful commit crime just as often as anyone else. And often times they work together. Watergate, the Iran-Contra affair, and CIA support of military coups against the democratically elected governments in Chile, Guatemala, and Nicaragua, including the murder of their leaders, as well as the many unsuccessful attempts to do the same in Cuba, were all conspiracies. The only reason some ideas are conspiracy "theories" is because insufficient evidence exists to prove them. Which you would expect, if the conspirators had covered their tracks well.
We know these things happened, and yet, being so long ago (20 years?) we conclude they are no longer relevant, and choose to continue to believe that something like that could never happen.

What is important is not proving whether or not the official version of 9/11 - physically - is accurate. To say that one should never question the purity of the American government is to insure that if they ever tried to do something like that, they would succeed. Indeed, if they were in anyway involved, the best way to prevent any real investigation, to prevent being questioned, is to accuse anyone who doubts them of being unpatriotic. This is exactly what Pop Mecanics and McCain have said (and I used to really like him). This is what millions of American citizens think to themselves.
This is what is written as if it went without saying in the original article here.
"Conspiracy theories as insane as that one, or worse, currently corrupt the political thinking of the great majority of people in the world"
Insane, as though it were not only false, but as if it were unthinkable.
Perhaps physically everything happened on 9/11 as the official version says. That doesn't mean the CIA couldn't have trained the hijackers, or provided funding, or even just suggested the idea in the first place.
I'm not saying those things happened. But to call belief in that possibility "insane" is dangerously close minded.
It is acknowledged that conspiracies actually happen, in politics as in organized crime. Considering that we must look at every possibility in as much detail as we can and not discount certain things as "conspiracy theories" just because we really really don't want to believe them.