Fundamentalism is a naive realist belief system which adhere to a moralism of adhering to 1) a truth which is reduced to a set of explicit truth assertions, characterized as one’s “beliefs” and 2) an ethic which is reduced to algorithmic practices, characterized as one’s “principles”.
To consider it a virtue to question or alter your beliefs and to always adhere to your ethical rules regardless of the consequences, and to call this virtue “faith” is to be a Fundamentalist.
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We are mistaken when we take a fundamentalist form of a religion as its purest expression. On the contrary, the purity of any form of fundamentalism consists of straining out precisely the essence of religion and retaining only the formal aspects, which are valuable solely as practical supports for religious life.
Religion is rooted in the finite but is oriented toward in infinite. Fundamentalism is hostile to everything beyond its finite system, and in this respect it is anti-religion.
Real religions are intersubjective. Nothing disrupts the apparent finitude of reality than other person who sees reality another way, revealing both one specific otherwise and the principle than an otherwise is always possible despite all inconceivability. To assume on principle that this other way is factually or morally wrong is to insulate oneself against the essential infinite Subject of religion.
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Every religion subjected to a Fundamentalist reduction ceases to be a form of that religion and becomes another denomination of Fundamentalism.