The deaths at Jonestown on 18 November 1978 killed more than nine hundred people and, with the murder of Congressman Leo Ryan and four others at the Port Kaituma airstrip, remained the largest deliberate loss of American civilian life until 2001. What happened afterwards shaped how every comparable group would be received.
The immediate effect was institutional. The anticult movement, a scattering of parents' groups through the 1970s, acquired a public warrant it had never had. Coercive deprogramming, the practice of removing an adult member by force for counselling, was defended in court and in the press on Jonestown's authority for most of the following decade. The Cult Awareness Network became the best known clearing house of that argument, and its end belongs to the story too: sued into bankruptcy in the mid 1990s, its name and files were bought at auction in 1996 by a buyer acting for parties connected to the Church of Scientology, so that callers seeking a warning reached the organisation they were being warned about.
The scholarly effect ran the other way. Sociologists of religion who examined the conversion research found no support for the brainwashing model the courts had been accepting, and the split that opened between the anticult movement and the academic study of new religions has never closed.
The archival effect is the most durable. The Jonestown Institute at San Diego State University, directed by Rebecca Moore, who lost two sisters in Guyana, holds the surviving tapes, documents and survivor accounts and has published them rather than curating a verdict from them.