I blame the Renaissance

It never fails. You try to point out that some supposed rule has no validity or make some empirical observation about actual English usage, and immediately comes the God-is-dead-and-everything-is-permitted outcry.

It happened today in a Facebook comment on my post "English has no scruples":  "does this mean that i'm longer entitled to cringe when i hear, 'where did you go to school at?' or 'i wish i would have gone?'" 

Nothing that I said about the language being what its users collectively make it obliterates the social and cultural dimensions. We recognize registers of language and adjust them for occasion and context. That's why "Aha, you linguists are hypocrites because you write in standard English" is a stupid argument. It's like saying that you're a hypocrite if you use baby talk with an infant but not with your boss.
You get to cringe at whatever you dislike, and so do I; that is part of the democracy of language. On a group trip to England a couple of years ago, I saw one of our party sitting at table with his cap on at afternoon tea in the Pump Room at Bath. He would have seen his wearing of denim and refusal to uncover as a mark of his authenticity, Brits would have thought "Another bloody American," and everyone would have been happy.
Much unnecessary trouble rises from an unexamined assumption that there is only one correct form of the language. For the peeververein, it's the standard written form, from which any variation in speech or writing is a solecism. Such people act as if there were, against all evidence, a single ideal form of the language, with clear and unchanging rules.
I think I know where that attitude comes from, and I blame the Renaissance.
The recovery of classical learning after the Middle Ages led to a great and exciting burst of creativity, but it created a problem. That learning was in two dead languages, Latin and Greek, which became ideals. You didn't study your own crummy vernacular at school. You already knew that. You studied Latin and Greek, which were held up as models, and which were unchanging.
This prestige value of Latin and Greek led to attempts to make the crummy vernaculars more "correct" by imposing Latin rules on languages with completely different grammars (thus the superstition about prepositions at the end of sentences). The French set up their Academy to regulate the language,* and Jonathan Swift wanted Robert Harley, Earl of Oxford, to get Queen Anne to do the same thing for English. Samuel Johnson, writing his "Plan of an English Dictionary" in 1747, proposed to fix (not correct, but make permanent) pronunciation and preserve the purity of the language. His "Preface," in 1755, is much humbler about his ambitions.
This misguided belief, that there is some Platonic ideal English out there that, like classical Latin and Greek, has unchanging rules of grammar and usage, has pernicious effects as we try to address questions of usage and make informed judgments about how to write and speak appropriately on different occasions. It yields either-or thinking, that you either enforce all the peever rules (you can't, by the way; they contradict) or there are no rules at all.
English is not a game of jackstraws; if you pull out a bogus rule, the language won't collapse in a heap.
*How's that hope-y, no change-y thing working out?