Conpiracy theories are widely deemed to be superstitious. Yet history appears to be littered with conspiracies successful and otherwise. (For this reason, "cock-up" theories cannot in general replace conspiracy theories, since in many cases the cock-ups are simply failed conspiracies.) Why then is it silly to suppose that historical events are sometimes due to conspiracy? The only argument available to this author is drawn from the work of the late Sir Karl Popper, who criticizes what he calls "the conspiracy theory of society" in The Open Society and elsewhere. His critique of the conspiracy theory is indeed sound, but it is a theory no sane person maintains. Moreover, its falsehood is compatible with the prevalence of conspiracies. Nor do his arguments create any presumption against conspiracy theories of this or that. Thus the belief that it is superstitious to posit conspiracies is itself a superstition. The article concludes with some speculations as to why this superstition is so widely believed.