People love conspiracy theories. They make up and passionately defend theories about events that have patently obvious explanations. Like the moon landings. The obvious explanation being that they happened exactly as they appeared. Like 9/11. What more explanation does one need than the evidence provided on live TV at the time? Was there a cover-up? I'm sure there was. But like the cover-ups surrounding JFK's assassination, they were designed to hide incompetence beforehand, panic at the time, and rash actions afterwards. The granddaddy of all conspiracy theories is creationism. How can something so important as me come about by chance?
Conspiracy theories are the modern, socially acceptable form of superstition. Studies have shown that the less control people have over their environment, the more prone they are to superstition. This should not be a surprise because superstition is a positive (though undesirable) behavior. The human mind making sense of the world and seeking patterns creates artifacts. Superstitions are the artifacts. Their presence has nothing to do with intelligence. They are due to lack of information, societal conformity and economy of effort. Most people don't spend time learning about or understanding things they don't need to. Most of the exceptions only learn or understand extra stuff that they are interested in.
Scratch the surface of anyone's understanding of the world and you will find lots of magical thinking. How does your TV work? How about the Internet you are using to access this post? They just work, and we don't need to understand the details if we don't want to. But importantly, we have a kind of story at the back of our minds about how these things work. That's the societal narrative. A shared set of short-hand explanations. When these explanations are grounded in evidence we call it science. When grounded in belief, we call it faith. When grounded in prejudice or ignorance, or nothing at all, we call it superstition. What all these share is a desire to discern cause and effect. A need to describe the structure of the world and the individual's place in it.
When the explanation for extraordinary events is inconsistent with people's life experience, they look for a new pattern that is more consistent. Not a bad thing on the face of it. But a lot of events are random or chaotic. Despite their importance, they were unanticipated because nobody thought they could ever happen. For example, the Japanese attack on Pearl Harbour. There are people who look at the evidence available before the event and conclude that the powers that be must have known. The evidence of impending attack went from suggestive a few weeks beforehand to persuasive a few days before to conclusive within an hour of the attack. Yet it was a total surprise. The idea that the Japanese would attack Pearl Harbour on that sunny Sunday morning never entered the heads of those in Hawaii until the funny looking planes dropped bombs that really went off. Since a Japanese attack was an idea that never formed, all the evidence that is so obvious in retrospect was dismissed or misinterpreted.
Unfortunately, if you want to believe that governments are on top of things, that things should work as they are supposed to, such failures are problematic. The Japanese shouldn't be able to sneak a fleet within striking distance of Hawaii undetected. A loser like Lee Oswald shouldn't be able to kill JFK with a cheap mail-order rifle. An avowed enemy of America like Osama bin Laden shouldn't be able to use the US air travel system to stage devastating attacks. But these events happened. Conspiracy theory bridges the gap. Roosevelt knew, but wanted the US in the war. JFK was killed by Castro, or the Mob, or Lyndon Johnson. The World Trade Center was blown up, not destroyed by an airplane. Because little things and little men shouldn't be able to cause big events. Big events need big causes. This proportionality is ingrained. It comes from early life experience and is an essential understanding of how the world works. So when the world doesn't work the way its supposed to, we fill in the blanks necessary to make it appear as if it does. But ascribing events to the evil eye, or curses, or black cats is declasse. The need remains, but the traditional methods are unavailable. We make up new ones.
Nobody is immune to magical thinking. We routinely blame cancer on luck or lifestyle. In fact, virtually every human over the age of 70 either has or will get cancer. Its almost universal. No matter how enlightened we imagine ourselves, people in 200 years will wonder at our astounding ignorance. Its no wonder then, that conspiracy theories proliferate. They are part of human nature. They will be around as long as we are.