Imagine Hamish McDonald, a Scotsman, sitting down with his Glasgow Morning Herald and seeing an article about how the “Brighton Sex Maniac Strikes Again.” Hamish is shocked and declares that “No Scotsman would do such a thing.” [Brighton is not part of Scotland.] The next day he sits down to read his Glasgow Morning Herald again and this time finds an article about an Aberdeen man whose brutal actions make the Brighton sex maniac seem almost gentlemanly. [Aberdeen is part of Scotland.] This fact shows that Hamish was wrong in his opinion but is he going to admit this? Not likely. This time he says, “No true Scotsman would do such a thing.”
—Antony Flew, Thinking About Thinking (1975)
Antony Flew was a philosopher who advanced this logical fallacy. When we face a counterexample, intead of accepting or rejecting it, we change the subject to exclude the specific case or similar cases.
A recent example:
“The protesters had been given drink and drugs.” ( no true libyan protests)
As everyone knows, no true Christian supports legalized abortion (or opposes it), no true muslim supports suicide bombings (or opposes them), no true Democrat supported the Iraq War (or opposed it)… etc