Many of these theories are clearly absurd, but some are plausible and others actually contain elements of truth. How can we distinguish among the amusing eccentrics, the honestly misguided, the avaricious litigants, and the serious skeptics questioning a premature consensus? With scientific claims, the only definitive answer is to reexamine the original research data and repeat the experiments and analysis. But no one has the time or the expertise to examine the original research literature on every topic, let alone repeat the research. As such, it is important to have some guidelines for deciding which theories are plausible enough to merit serious examination.
One valuable guideline is to look for cascade logic in conspiracy arguments (Susstein and Vermeule 2008). This occurs when defenders of a conspiracy theory find it necessary to implicate more and more people whose failure to discover or reveal the conspiracy can be explained only by their alleged complicity. Another guideline is to look for exaggerated claims about the power of the conspirators, claims that are needed to explain how they were able to intimidate so many people and cover their tracks so well. The more vast and powerful the alleged conspiracy, the less likely that it could have remained undiscovered.
Source: Csicop - "The Conspiracy Meme"