For the past two and a half centuries, from Robert Lowth to Henry Fowler to Strunk and White, self appointed language scolds have been trying to tell us how to speak our mother tongue. Fortunately, they have not much influenced the actual evolution of English. Unfortunately, they have made a lot of perfectly capable native speakers feel, incorrectly, that they weren't competent in English, and more importantly, made those native speakers feel unhappy about that imagined non-competence.
They have done so by confusing matters clearly in the realm of class and status with issues of linguistic capability, eloquence, style, and beauty.
The occasional (and usually unfortunate) practical need to speak or write in a formal register of conventional standard English is one thing, and is part of our larger ability to navigate the complicated shoals of the social structures we live in, but our ability to communicate fluently both in speaking and writing day to day with the people we are at ease with is quite another. We learn our language in an informal register as children, but even at that level we learn some class and status language modifications. I grew up addressing most (but not all) of my elders as "ma'am" and "sir." Happily, this custom has since mostly disappeared. (Personally, I am delighted when I am not addressed as "sir" now that I am in my dotage.)
The custom of my Texas childhood was in the realm of what was then living English, a regional variety, of course, and the current standard of sirlessness and ma'amlessness, are part of today's living language.
The kind of language prescriptions that I am talking about are the heroic but hopeless efforts to revive the dead. Or worse, to revive mythological language standards that never were alive. If I were to say Strunk and White stood for Zombie Standard English I would enrage all those people who imagine that the passive voice is a bad thing (often without knowing very well what the passive is) and that a split infinitive is a moral transgression; but if they can feel rage, hey, it's a sign of life, at least. Alas, that rage only drives them to write a letter to the editor full of peeves about the sad state of our language.
The "prescriptive ideologues" (as Geoffrey Pullum calls them) defy the barbarians from behind the ramparts of correct English, or what you can more accurately call a prestige dialect of modern English, but as imagined by the ideologues, not necessarily as spoken or written even by them.
Prescriptivist zealots will insist that it's not just a matter of class and status and hierarchy, and the occasional practical requirement that we submit to the tyranny of class-and-status speech demands, but a matter of actual standards, the notion that there is an underlying…something…somewhere, justifying the dictatorship of long-dead grammarians. What might that be?
Well, Pullum classifies such standards-claims under headings of authority, esthetics, logic, efficient communication, self-discipline, and a posited golden age of English for which a self-selected few now yearn. (I think I may have forgotten one.) The problem obviously is that none of these constitute a bedrock that anyone could call objectively real. Several of them, like esthetics and alleged requirements of communication, are not only bogus but blown out of the water by the tortured writing and fractured logic of most of the standard-worshippers themselves. (WRT alleged "logic", anyone who has ever learned a European language knows that a double negative does not somehow imply a positive except to a computer, and an unimaginatively programmed one at that.)
Turtles all the way down.
You'll notice this is written mostly in a formal register of standard English. I apologize.