"No true Scotsman"
is the term I've heard for that particular argument.
But the term I'd prefer is "Margaret Thatcher is a Man". Back when Maggie was running the island, some feminist was going on about how peace and prosperity would reign when women were in charge, and somebody in the audience mentioned that Margaret Thatcher didn't seem to be bringing the peace and prosperity. The feminist replied "Margaret Thatcher is a Man".
Actually, that island has some history of female rulers. Generally, they have been more fierce than nurturing.
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I think it's perfectly clear we're in the wrong band.
(Tori Amos)