You are clearly right that conspiracy is hard. And yet, it is not impossible. Plenty of major events are caused by conspiracies, from the assassination of Julius Caesar to the recent coup in Thailand. In addition, to truly prevent a conspiracy, it is often necessary to do more than merely reveal it; if the conspirators have plausible deniability, then revealing (but not thwarting) the conspiracy can actually strengthen the plotters hands, as they can now co-ordinate more easily with outside supporters.

Successful conspiracies, like any other social organization, need incentive compatibility. Yes, it's easy to find out the secrets of the Scientology cult. Not so easy to find out the secret recipe for Coca Cola, though.