The problem is that historically conspiracies fail, someone always gives the game away in the end. People are very bad at keeping secrets because we are social animals. I have no problem believing in real proven conspiracies. So for example I don't believe that Eisenhower knew about Pearl Harbour before the attack because it makes no sense. A thwarted attack would have had the same effect as a successful one. The previous poster seems unaware that for most people a brief search on the internet is not going to take them to some fringe website but to more traditional online encyclopaedias that make use of evidence rather than hearsay and conjecture.
As per usual, evidence is the thing that makes the difference to thinking people. Contrary to the previous poster I think a more educated person is much more likely to be sceptical than the sort of swivel eyed loon that believes in every paranoid fantasy out there.