When 'anything goes' in linguistics

At the Language Log there's a nice list of posts about the descriptive/prescriptive divide in linguistics, and I will put here excerpts of a few of these articles.
 
English grammar: not for debate:

A case from one of Engand's greatest ever poets, dated 1590, rather puts a damper on the theory that this is a matter of recent sloppiness, does it not? Probably not. I confess I cannot figure out what could convince this man. (...) His view may really be just that he personally dislikes encountering the verb warn without a noun phrase complement. He may be calling it ungrammatical merely to make his personal peeve sound more like an objective opinion.

Logical prescriptivism:

In the case of word formation and its connections to sound and sense, logic is an especially unreliable guide. And of course the English writing system is a complex pattern of overlapping historical layers with sporadic intrusions of reform, for which the appropriate mode of analysis is more geological than logical. (...) This is a sadly undemocratic fact, since it means that no reliable short-cut, in the form of a short list of simple rules, is available to those trying to master a standard language. There's no real alternative to doing a lot of reading and listening.

Usage advice:

There have been a couple of relevant posts over the years, but what this reader really needed was a reminder to check his copy of the Merriam-Webster's Dictionary of English Usage (or the concise edition of the same work). (...) If you don't already own it, you should go buy this book. And just as important, when a question of English usage comes up, it's one of the first places that  you should look for an evidence-based opinion.

The origin and progress of linguistic norms:

There are apparently a few people out there who object to the whole notion of a standard written language, or believe that it's wrong to urge people to learn one; but none of these people post on this site, as far as I know. (Some of our commenters may feel this way, I'm not sure.) At the other end of the spectrum, there are apparently some people who believe that all linguistic varieties that deviate from (someone's idea of) a standard should be ruthlessly suppressed. But most purveyors of usage advice, of whatever species, simply believe that the formal written language should be learned and used in certain contexts;

Contractual Grammar:

There's a presupposition that leaving people to work such things out for themselves is intolerable, either morally or practically, so that the principles must be codified and enforced by some authority.

The alternative — which most modern linguists prefer — is not to treat language as unsystematic or unconstrained, but rather to view it preferentially as a natural rather than an artificial phenomenon, what Hayek called a "grown" or "endogenous" or "spontaneous" order, rather than a "made" or "exogenous" or "artificial" order. (...) In this respect, descriptive linguists are libertarians, or perhaps classical liberals, while prescriptivists are authoritarian rationalists.

Progressive prescriptivism?:

In modern times, it's common for would-be linguistic authorities to pretend that they're holding the line against degenerative change, even when they get the history backwards. But John Dryden initiated the condemnation of sentence-final prepositions on the grounds "that the language, wit, and conversation of our age, are improved and refined above the last". Perhaps this style of progressive prescriptivism influenced some later grammarians to see the be/have change as a step forward into a better future, rather than a symptom of how far kids these days have fallen.

My reading list usually goes to my other, minimalist blog, but this discussion is relevant since in Brazil this is a hot topic: there is a sanctioned textbook defending grammatical errors and saying that otherwise would be prejudice, and neither the author nor the Ministry are retracting. It's one of the Brazilian versions of the "teach the controversy", forgetting that schools are for many the only place where they'll have contact with the language as a subject of inquiry, and are their best opportunity of improving their lives.