Epistemological approaches see the study of conspiracy theories as a branch of epistemology and insist that each theory should be judged on its evidential merits. These approaches oppose any general presumption that conspiracy theories are false or unwarranted. In this talk, I'll be suggesting that conspiracy theories are best understood in politico-ideological rather than epistemological terms. They are fundamentally forms of political propaganda. They give expression to, and promote, the ideologies with which they are associated. In the case of anti-Semitic conspiracy theories, these are extremist ideologies. Anti-Semitism is the original sin of conspiracy theories, and philosophers who claim that every conspiracy theory should be considered on its merits betray a fundamental misunderstanding of what conspiracy theories are and how they function.