"In this sense its predecessors are not really the original enlightenment rationalists, but the dubious touchstones of ‘60s-hangover California--Scientology and Dianetics, Werner Erhard and est,"

There's also some historical ties between the golden age sci fi that Yudkowsky was steeped in growing up (no doubt many other Rationalists too) and these kind of culty self-improvement groups that promise almost supernatural expansion of mental abilities. Alex Nevala-Lee's book "Astounding: John W. Campbell, Isaac Asimov, Robert A. Heinlein, L. Ron Hubbard, and the Golden Age of Science Fiction" has some good info on this, especially how Campbell, an editor who was hugely influential on the development of science fiction stories after taking over the magazine "Astounding" in 1937, went in for all sorts of "new psychological technology" schemes including the beginnings of L. Ron Hubbard's Dianetics (Nevala-Lee also has some posts on Campbell and Dianetics on his blog at nevalalee.wordpress.com… ). Also see the article on "self-help supermen" in WWII era sci-fi, which talks about Campbell's influence, at jstor.org/stable/10.562…