Conspiracy theories should be neither believed nor investigated - that is the conventional wisdom. I argue that it is sometimes permissible both to investigate and to believe. Hence this is a dispute in the ethics of belief. I defend epistemic ‘oughts’ that apply in the first instance to belief-forming strategies that are partly under our control. I argue that the policy of systematically doubting or disbelieving conspiracy theories would be both a political disaster and the epistemic equivalent of self-mutilation, since it leads to the conclusion that history is bunk and the nightly news unbelievable. In fact (of course) the policy is not employed systematically but is only wheeled on to do down theories that the speaker happens to disl...