Ended up following my site traffic and bumped into this Live Journal entry.
Conspiracy is one of the first refuges of woo. It's a easy defense mechanism to create a "THEM" who are against sunshine and bunnies when your pet hypothesis fails all the relevant tests. People naturally want to think in terms of agency: That someone or something causes certain things for a reason. It's a useful instinct when you're dealing with sharp-toothed critters on the savanna, but it's easy to apply the principle when you should instead consider the possibility that you're wrong.
Woos take that easy path all the time, no matter how silly or cynical the conspiracy they invent is. Alties seem to believe that doctors cover up miracle cures because they're greedy bastards with no family or friends who might be affected by those diseases. 9/11 Twoofers believe that thousands of people with useful evidence can all be easily silenced with threats or money. Ufologists believe that men in cliched black suits and sunglasses show up to perform cover ups. Heck, any unpopular theory often gets people complaining about "political correctness" as if that has anything to do with their lack of basic plausibility or data.
It's often an ego-saving defense mechanism. They backed the wrong horse, and don't want to admit it. So, they make a conspiracy so that they can play victim: They're right, and anyone who says otherwise is obviously an evil member of the conspiracy out to suppress the truth they're privileged to be in on. They're above the "sheeple" who are simply programmed to respond to the impractical idea that evidence matters.
It's the ultimate ad hoc hypothesis: Why can't they find evidence? Because the conspiracy covers it up. Why do the skeptics' predictions come true? Because they're in on the conspiracy and arranged things in their favor. Conspiracies can be invoked to explain anything that goes against a woo hypothesis's predictions.
It's Hollywood! Reality's boring when you can be the star of your own suspense thriller flick! In the movies, it's never the obvious answer! Things are never what they seem, EVAR! Of course, reality doesn't operate by the rule of drama: Sometimes things really are what they seem to be. Sometimes the obvious answer is the correct one. Reality isn't a movie genre.