"Prescriptivist wisdom" - well it's certainly prescriptivism, but it matters what kind, as evidenced by the fact we all tolerate spelling prescriptivism just fine. Those of you who use this construction seem to feel that it's a matter of grammar, and that the rule against using it is in the same class as e.g. not splitting infinitives.  I.e. language prescriptivism. But it is meant to be manners prescriptivism - in the same class as saying "thank you" when someone does something nice for you, if of less gravity.