Extremists who have been well educated in science are quite common, but nevertheless puzzling. How can individuals with high levels of scientific education fall prey to irrationalist ideologies? Implicit assumptions about rationality may lead to tremendous and conspicuous developments. When correction of social deficits is seen as a pressing problem, it is quite common that individuals conclude that some religious or political system contains the all-encompassing answer, if only it is applied with sufficiently high standards. Implicit assumptions about rationally high (...) standards often demand consistency, system and justification. The strict application of these standards to political and/or religious systems leads quite readily to extremism. J. L. Talmon has shown how the rationality of the Enlightenment led to intolerance, dictatorship and torture. The Enlightenment view of rationality can also encourage irrationalist ideologies and extremism: it leads individuals to conclude that various religions and/or political systems contain all encompassing answers, if only they are systematic, coherant and justified. Alternative theories of science and rationality, which view rationality as critical, partial, and progressive, and which seek to improve imperfect standards, can help avoid the unintended support of extremism rendered by established views of rationality. Unfortunately such theories meet enormous resistance: they call into question well-established canonical doctrines. (shrink)