I suspect puckish intent in the incomparable Kory Stamper's post at harm-less drudg-ery on the prescriptivist-descriptivist divide. Though I have commended "A Compromise: How To Be A Reasonable Prescriptivist" to you previously, I would like to admire a couple of the finer points. 

Though the overall intent and tone are as irenic as anyone could wish, I noticed a few sly touches guaranteed to rattle the peeververein. A terminal preposition was the least. There was also a "the hoi polloi." There were a couple of split infinitives, and when Ms. Stamper splits an infinitive, she cleaves it with a broadaxe, and no mistake. 

But the guaranteed peevebait was a singular they, and indeed (really, you must look at the comments as well as the article) a reader styled as calitri rose to the bait as a mature trout to a Smithwick Rattlin' Rogue.

Calitri's contention, and really the only argument put on offer, though repeatedly iterated, is that they is a plural pronoun, and only that. Case closed, docket cleared, court adjourned. Calitri is an essentialist. Words have some Platonic essence apart from the way people use them, and violation of that essence is, and can only be, an error, a proof of ignorance, a mark of sloppiness, or a sneer of utter disregard for the settled conventions of civilized society. 

But a little thought would show that words are what people choose to make them. If enough speakers and writers over an extended time decide to use a plural pronoun in a singular sense, then, by gum, it takes on a singular sense. Calitri would do well to ponder that that is precisely what happened to the pronoun you. But I'm not waiting for the penny to drop. 

Great fun, anyhow.