It is sometimes argued that only the religious could really comprehend religion and that, therefore, the irreligious ought to abstain from criticizing religion or religious beliefs. In other words, a peculiar worldview can only be fully understood from within and should thus be criticized only from within.

This argument can easily be refuted by a reductio ad absurdum. If it were true that peculiar worldviews could only be comprehended by those supporting them, respectively, and ought to be criticized only by them, then it would follow that fascism could only be fully understood by fascists, that communism could only be fully understood by communists, that conservatism could only be fully understood by conservatives, and so forth, so that everyone who is not a fascist ought to abstain from criticizing fascism, everyone who is not a communist ought to abstain from criticizing communism, everyone who is not a conservative ought to abstain from criticizing conservatism, and so on – which would be absurd (I call this the ‘first-person knowledge requirement fallacy’); quod erat demonstrandum.