Dear Mr. Keller: Last night on the “PBS NewsHour,” they had a story about some Los Angeles Times reporters who uncovered corruption in a nearby, small city in California. The newspaper eventually received a Pulitzer Prize. That is what you can have if you will talk with me. Within one hour, I will convince you and your staff that Lee Oswald did not assassinate President Kennedy. Then, I will give you the evidence for the real killers, and how the cover up could be perpetrated. It is a great story, fully documented and supported with facts, many from the Warren Commission itself!!

That e-mail landed a few weeks ago. Even if you are a card-carrying member of the reality-based community, even if you regard the liberal use of exclamation points as a symptom of emotional instability, there is a little voice, a very, very little voice, that whispers, in the few seconds before you push “delete”: “What if he’s right? There’s always been something fishy about that assassination. What if the e-mail I am reflexively sending to the trash file is the story of a lifetime?”

Humans live along a continuum from doubt to faith. Wander far enough in the direction of faith and you reach the land of Nostradamus and of the Rapture (recently postponed). Wander too far in the other direction, past cynicism, through misanthropy, and you get to more or less the same zone of credulity: Osama bin Laden isn’t dead, President Obama isn’t American, global warming is a hoax.

Recently we have pivoted from one conspiracy theory (the plot to hide our president’s foreign birth) to another (the plot to frame Dominique Strauss-Kahn, the French banker and Socialist candidate-in-waiting known by his monogram and for his predatory eye for women). More than half of the French people surveyed in the immediate aftermath of D.S.K.’s arrest told pollsters that he was set up. This belief was held by men and women, by the most educated and the least. Among Socialists — whose ideology might suggest a little empathy for a working-class African immigrant charging assault by a rich, powerful capitalist — an astounding 70 percent believed their party darling was the real victim. People who would happily accept the label “intellectual” were quick to surmise that the scandal was somehow cooked up by President Nicolas Sarkozy (with the help of French-hating Americans) to bring down a rival on the left.