No one, for example, takes Gibbon's argument on the Fall of the Roman Empire seriously anymore; similarly, no one takes the argument that Islamic cultures economically failed (in comparison with Europe) because of anti-capitalist religious precepts seriously either. Yet both were a part of serious teaching a few decades ago (the age of some textbooks).
I remember one textbook I had as a child argued that the reason that Lowland Scots prospered in comparison with Highland Scots was due the Protestant work ethic bestowed upon them through Prebyterianism - in comparison, the Highlanders succumbed to their lethargic Catholic proclivities. Hilarious in hindsight, but slightly disturbing as real teaching.
If bankers can count, how come they have eight windows and only four tellers?