At Psychology Today Blogs, Jade Wu takes a look at why persons are susceptible to conspiracy theories and how said theories take root. Here’s one of the reasons she offers as to the latter factor (emphasis in the original); follow the link for the complete article and citations.
2. It’s not about the specific content. You may think how well a conspiracy theory takes root in someone’s mind depends on how credible the theory is, but content really isn’t that important here. Whether someone adopts a conspiracy theory or not depends more on their overall proneness to believe in conspiracies in the first place.
In other words, the act of believing in conspiracy theories is its own fuel. The more we believe in one, the more likely we are to believe in others, even if they’re contradictory.