There are three reasons to lack belief in something. I present them in decreasing order of strength.
The first situation is when the belief requires a great many ad hoc assumptions, and simultaneously, there is a large quantity of evidence against it. An example of this is astrology. A belief in astrology requires that you not only break Ockham's Razor (the principle that the simplest explanation that adequately explains all of the facts is the most likely to be correct), but that you ignore the many controlled studies showing there to be no correlation whatsoever between a person's astrological sign and his/her personality.
The second is when there is no particular evidence against the belief, but also very little for it; and it also runs up against the sharp edge of Ockham's Razor. Belief in the existence of Bigfoot is one of many examples of this sort of thing. The evidence, such as it is, consists of fuzzy videos and photographs, footprints, and anecdotal stories, all of which are obvious candidates for fakery. The simplest consistent explanation -- that the sightings of Bigfoot are hoaxes -- requires far fewer assumptions than the idea that there is a large primate in the forests of the Pacific Northwest that has somehow never left behind a single piece of unequivocal hard evidence.
The third, and weakest, is when we simply lack data. For example, I am sometimes asked by my biology students if the vocalizations of whales and dolphins are actually language. My answer: we don't know. Language -- a system of arbitrary representational symbols expressing concepts -- is only easy to recognize if you know the rulebook. In this case, it may be that whales are using language, or it may be that their sounds are simply non-symbolic communication, such as we see in the barking of dogs. The bottom line is that at present, there is no reason to believe that whales are using language, but also no particular reason to disbelieve. Ockham's Razor remains unbroken either way, so we simply suspend judgment and wait for more evidence to surface.
Which brings me, unfortunately, to Osama bin Laden.
When the US announced a few days ago that bin Laden had been killed by a task force of SEALs, the first reaction was one of relief. Justice, people said, had been done at last. President Obama's approval ratings jumped, and even Glenn Beck gave some grudging props to the administration. But then came the announcement that bin Laden had been buried at sea, and the photographs of bin Laden's corpse would not be released. The explanation was that the hasty disposal of the body was to render it impossible for bin Laden's followers to turn his burial site into a shrine, and the decision not to make the photographs public was based on a desire not to inflame hostility and retribution on the part of devout Muslims who might consider the posting of such gruesome photographs as a sign of disrespect.
And then photographs appeared online anyway. They were, the posters said, leaked from military sources. Analysts were quick to point out that they were photoshopped fakes; one of them, in fact, was an amalgam of an image of bin Laden and a still of a corpse grabbed from the movie Black Hawk Down. Conspiracy theorists began to squawk that the whole thing smacked of a coverup. Orly Taitz, now that President Obama has released his birth certificate, was apparently fishing around for something to do after she ruled out "shut the hell up and get a real job," and decided to join the fray. On her website, she asks the question of why bin Laden wasn't properly ID'd, or (better yet) taken alive. I guess she's waiting for bin Laden's long-form death certificate to be released.
The theories began to get wilder and wilder. In an interview, Steve Pieczenik, who was Deputy Assistant Secretary of State in the 1980s and 1990s, has claimed that the whole thing is a red herring -- that bin Laden actually died in 2001 of Marfan Syndrome, shortly after 9-11. Any videos and audio clips of him after that time were either fakes or were recordings made prior to his death. He has stated that he is prepared to testify before a grand jury that this is true.
Allow me to point out that he is also the author of psycho-political fiction. I'll leave you to decide if this is relevant.
Other conspiracy theorists claim that bin Laden was killed last year, and his body frozen, to be trotted out to give the President a boost when (1) the 2012 election was approaching, (2) his ratings appeared to be falling, or (3) both. Taitz, while not specifically espousing this theory, has wondered aloud how it can be a coincidence that the whole birth certificate thing was resolved only a few days before bin Laden was killed. "It was a move calculated to distract the public," Taitz said, which I suppose turns her from a "birther" into a "deather."
And then, of course, there are the people who believe that bin Laden is still alive, and that the whole thing was a hoax from beginning to end.
So, where along the lines of belief does all of this fall?
Well, first of all, let's look at the evidence we have -- the administration's story and the pictures of the compound. Not, I will admit, a wealth of hard data to go by. So failing concrete evidence, we have to fall back on Ockham's Razor. What explanation fits the known facts, while requiring the fewest ad hoc assumptions?
We have, on the one hand, a story that some Navy SEALs flew into Pakistan in a couple of helicopters, broke into some random house, ran about firing their weapons, and didn't kill Osama bin Laden (who either was elsewhere at the time, or else already dead, depending on which version you go for). Having thus successfully not killed bin Laden, they got back on their helicopters, perhaps with the body of someone else, and flew out to waiting ships, where a fake funeral was held. A great many soldiers, and their commanding officers, were complicit in this coverup, as presumably all of the people in charge of the raid would have to have known perfectly well that bin Laden wasn't there (and if they didn't before, they figured it out pretty quickly afterwards). Despite the number of people who at this point know that it was all faked, no one has spoken up. As far as the purpose of this jiggery-pokery, all of it was done purely to boost Obama's ratings.
On the other hand, we simply accept that in the default of evidence to the contrary, the administration's story is substantially true.
So, we basically have a case of Bigfoot here. Is it impossible that bin Laden is still alive, or that he died years ago? No, any more than it is impossible that Bigfoot exists. But there is a difference between "possible" and "probable," a distinction on which many people seem to be unclear. If you have an improbable, convoluted explanation for something, it isn't enough just to say "it could be so." In these situations, we invoke another principle -- ECREE, or "Extraordinary Claims Require Extraordinary Evidence." It is not the responsibility of those of us who disbelieve in bin Laden death conspiracies to prove our case, any more than I should be required to "prove" why I don't believe in Bigfoot. The bottom line is, if you think President Obama is lying, show us your evidence. Saying "he could be" just isn't sufficient.