Journalist are often sent to places — a war zone, a natural disaster, or a crime-ridden slum — that are physically scary. Those assignments routinely win prizes.
Sometimes they may be asked to cover a story that is intellectually scary. Those assignments are less dramatic but can reveal more about human nature.
Perhaps the most intellectually scary assignment I have had in recent years was to cover a meeting of the so-called "9/11 Truth Movement" in the East Village, New York.
This gruesome assortment of conspiracy theorists insists that the attacks on the US of September 11, 2001 were an inside job.
It is easy to mock this deluded gang of ageing hippies, anarchists and anti-Semites.
I was an eyewitness to the 9/11 attacks, reporting for this newspaper. I stepped out of my local newsagents in New York just seconds after the first plane hit to see a fiery gash above me in the north tower of the World Trade Centre.
I asked the nearest passerby what had caused the flaming hole, assuming it had been a bomb. She told me she had seen a big silver plane fly straight into the building.
Any doubts were expunged minutes later when the second hijacked airliner hit the south tower, all broadcast live on TV.
But to those gathered in a church hall in the East Village, those reports — even the TV pictures — were all part of an elaborate government cover-up.
The assembled conspiracists quickly agreed that the twin towers had been packed with explosives by the Government, since jet fuel did not burn hot enough to melt the buildings' steel frame.
There was a broad consensus that the Bush family and the Kuwaitis, by virtue of their representation on the board of the trade centre's security company, must have been in on it.
Then a woman stood up and shouted: "What about the Koreans?"
For a moment, the conspiracy theorists were flummoxed.
"The Koreans also had a seat on the board," she protested.
After a brief pause to digest this new information, the 9/11 Truth activists welcomed her to the fold.
I found the event not just disconcerting but also extremely revealing. I had never understood better how so many Germans could have embraced the crackpot theories of Nazism.
America is now again witnessing the advent of a crackpot movement in the so-called "Birthers".
This group insists, despite ample evidence to the contrary, including a birth certificate and two contemporaneous birth announcements in Honolulu newspapers, that Barack Obama was not born in the United States and is therefore constitutionally ineligible to serve as President.
I have taken more interest than most in Mr Obama's background. A week before the election, I found his Kenyan aunt living in a council flat in Boston. His uncle "Omar", who has used the name Obama Onyango, is still, I believe, living in the United States unidentified as a presidential relative.
The "Birther" theory has been thoroughly discredited. It has even been disowned by the chairman of the Republican Party.
I was not surprised, therefore, to discover some overlap between the "Birthers" and the 9/11 Truth Movement.
Philip Berg, a maverick Pennsylvania lawyer, once filed a suit against President George W. Bush alleging that the World Trade Centre was destroyed by a "black-op shadow government designed to replace the elected government of the United States".
More recently, he has turned his attention to filing lawsuits unsuccessfully challenging Mr Obama's citizenship.
It is important that we understand the hallmarks of such conspiracy theories, so that we can recognise them for what they are.
James Meigs, editor-in-chief of Popular Mechanics magazine, which has published a book entitled Debunking 9/11 Myths, explained to me that conspiracists usually seize on a single suspicious fact on which to build their whole edifice of paranoia.
Mr Meigs suggested that, armed with this stubborn fact that does not seem to fit, conspiracy theorists separate themselves from the crowd and elevate themselves into brave seekers after truth.
In the case of the World Trade Centre, the trigger was the burning temperature of jet fuel. (The flaw in the logic is that the steel did not actually need to melt for the buildings to collapse.)
For the "Birthers," it is the fact that the 2007 Hawaii birth certificate released by the Obama campaign last year was not the 1961 original. (FactCheck.org has examined the original 1961 birth certificate and says it has a raised official seal.)
Unfortunately, no amount of rational argument will convince the Birthers or the 9/11 Truth activists that they are wrong. Every denial merely feeds their conviction of a cover-up.
These are indeed intellectually scary people.
