No true Scotsman
No true Scotsman is a logical fallacy where someone attempts to avoid association with an unpleasant act or person, asserting that the person doing such an act is not a true member of the group.
The philosopher Antony Flew coined the term, giving an example of a Scotsman who saw a report of a series of sex crimes taking place in Brighton then states that no Scotsman would act in such a manner. Later the Scotsman is presented with a newspaper report of a similar crime being perpetrated by a Scotsman, to which he responds that no true Scotsman would do such a thing.
It is widely used by some religious apologists and political ideologues when attempting to apologise for the actions of others who hold their beliefs. Liberal Christians have claimed, for instance, that the more extreme end of fundamentalist Christianity are not truly Christian, and liberal Muslims have done likewise regarding Islamic extremists.