This paper describes the beliefs and practices of the 911 truth movement, who believe that the World Trade Center collapse was caused by a "controlled demolition" and not by the hijacked airplanes. They try to expose the lie of the "official conpsiracy theory" of hijackings. The "truthers" have a coherent belief system, virtual communities and demonstrations, and enemies such as the mainstream media and those trying to "debunk" them. An ethical issue for anthropologists is whether we should accept the truthers as simply another "alternative" view, or try to criticize and counteract them in the name of science and reason. Presented in several forums, most recently at the American Anthropological Association, Nov 2010.