The No True Scotsman fallacy is a well-used fallacy in debates about religion with religionists. As wiki defines:

No true Scotsman is an informal fallacy, an ad hoc attempt to retain an unreasoned assertion.[1] When faced with a counterexample to a universal claim, rather than denying the counterexample or rejecting the original universal claim, this fallacy modifies the subject of the assertion to exclude the specific case or others like it by rhetoric, without reference to any specific objective rule.

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