I have posted this earlier,
I believe a good workable conspiracy plan must have the following to have any real chance of success so before you "believe" in a particular conspiracy think carefully if it has the following,
1: Very few people involved, just barely enough to get the job done and maintain secrecy. (This is just about impossible because someone will always spill the beans at some point either through carelessness or a fit of conscience, I mean if the president of the United States of America cant enjoy a nice quiet little blow job in the privacy of the oval office bathroom then what hope do conspirators have who are trying to take over the world?!)
2: The people involved will be dedicated to the conspiracy and/or have a vested interest in it's success and will benefit or see a benefit from their actions. (Political, religious, social or financial etc)
3: The people involved will willingly remain silent and protect each other and the conspiracy because of the above. (The threat of physical violence against a participant or their family etc is very risky to the conspirators and no guarantee of silence.)
4: The mechanics of the conspiracy must be as simple as possible and above all, subtle...
Putting it simply, if it was a real conspiracy, you might not even know about it...
Nowadays everyone seems to know "the truth" with the exception it seems of those who were actually involved...