In my post entitled Clarke's Third Law, I talked about my search for a reason that people are so willing to believe in hoaxes. In that post, I posited that the difficulty in understanding the science behind much of which we deal on a daily basis makes simpler theories easier to believe, even though they are completely wrong.
However, I realized today that there is another factor that can't be discounted. Many of these theories posit some sort of ill intent: the government puts fluoride in the water to control us; or vaccines are a plot by the medical establishment to dig deeper into our pockets.
Perhaps it's that ill intent that makes people want to believe. Human beings love to judge. We like to find moral failings in others (and I won't say why, because the reasons can be myriad.) So we get a certain salacious delight in these theories and want to believe them.