The typical explanation of an event or process which attracts the label ‘conspiracy theory’ is an explanation that conflicts with the account advanced by the relevant epistemic authorities. I argue that both for the layperson and for the intellectual, it is almost never rational to accept such a conspiracy theory. Knowledge is not merely shallowly social, in the manner recognized by social epistemology, it is also constitutively social: many kinds of knowledge only become accessible thanks to the agent's embedding in an environment that includes other epistemic agents. Moreover, advances in knowledge typically require ongoing immersion in this social environment. But the intellectual who embraces a conspiracy theory risks cutting herself off from this environment, and therefore epistemically disabling herself. Embracing a conspiracy theory therefore places at risk the ability to engage in genuine enquiry, including the enquiry needed properly to evaluate the conspiracy theory.