A quote from Karl Popper:
"...‘conspiracy theory of society ... is the view that an explanation of a social phenomenon consists in the discovery of the men or groups who are interested in the occurrence of this phenomenon (sometimes it is a hidden interest which has first to be revealed), and who have planned and conspired to bring it about. This view of the aims of the social sciences arises, of course from the mistaken theory that, whatever happens in society—especially happenings such as war, unemployment, poverty, shortages, which people as a rule dislike—is the result of direct design by some powerful individuals and groups. ...
The gods are abandoned. But their place is filled by powerful men or groups—sinister pressure groups whose wickedness is responsible for all the evils we suffer from—such as the Learned Elders of Zion, or the monopolists, or the capitalists, or the imperialists."
And, to head off one of the obvious complaints:
"I do not wish to imply that conspiracies never happen. On the contrary, they are typical social phenomena. They become important, for example, whenever people who believe in the conspiracy theory get into power. And people who sincerely believe that they know how to make heaven on earth are most likely to adopt the conspiracy theory, and to get involved in a counter-conspiracy against non-existing conspirators. For the only explanation of their failure to produce their heaven is the evil intention of the Devil, who has a vested interest in hell."