“No Scotsman ever puts sugar on his porridge oats”
“But Angus McSporran does!”
“Ah, then Angus McSporran is not a true Scotsman!”
Anthony Flew is responsible for exposing this fallacious type of argument, in his 1975 book Thinking About Thinking.
I read this in “Philosophy Now” where I also see that this little book should be read by everybody, although it will annoy me because a large proportion of the examples are taken from muddles in what might well be seen as left-wing thinking.
The no true Scotsman thing tickles me, so I'll read the book anyway.
Flew has recently died. He was an atheist who a few years ago famously converted to Christianity or at least to Deism. No true atheist would do such a thing, therefore ....