It struck me that grammatical prescriptivism bears a very similar relationship to linguistics as does mysticism to science. This can be analyzed from a philosophical as well as a political perspective.
[Edit: It was pointed out to me that my use of the word "mysticism" here is inappropriate. By it I mean any sort of magical or supernatural thinking, rather than the more usual notion of special states of consciousness meant to put one in touch with the divine. Additionally, a few edits were made towards the end to make my main point clearer.]
Both mysticism and prescriptivism operate on the basis that there need to be certain well-defined rules for how the world works (even if that rule is just "because that's how God did it"). In each case, there is a very strong reluctance to let go the reigns of reality, as it were, for fear that utter chaos would result. The mystic needs their magical system to keep their crops growing, their cities plague-free, and their soul saved. Similarly, the prescriptivist needs strict usage rules to make sure their sentences are (what they consider to be) optimally readable, socially and politically correct, and up to some abstract standard, lest all semblance of readability and communication disappear. In each case the advocate of such rules fails to see that their rules are arbitrary and related to reality only through social convention and particular modes of thought. They miss the point that their devotion to the actual facts of the world is outweighed by their devotion to an already-given system of rules. The rules of both the mystic and the prescriptivist are arbitrary rules.
Now, there is certainly a place in society for arbitrary rules. In the United States, people drive on the right side of the road. If we don't all agree to do so, there will be a lot of head-on collisions. But we don't look at England or Australia and scream that they are doing things wrong and need to change which side of the road they drive on. There may be a bit of inconvenience in shifting from one to the other, but no one in their right mind would claim that there is a correct side of the road to drive on, and an incorrect one, and that America is correct and England incorrect. They are just arbitrary stylistic choices. (Well, maybe.)
Similarly, religious prescriptions are arbitrary rules insisted upon by people with
an interest in standardizing the behaviors of members of a given
community (including thoughts and utterances). And grammatical prescriptions ("no dangling modifiers", "no stranded prepositions") are arbitrary rules that have been historically insisted upon by people with an interest in standardizing the grammar of a given language.
Of course, I am assuming my reader agrees with both of these assertions. The first one is easy for many people to accept (or at least grant for the sake of argument), as opposition to mystical ideas has a long and proud history, in the form of rationality and science. The second one, though, has its basis in the very young and very much still growing field of linguistics, whose goals, methods, and justification few people have been exposed to, and fewer still understand. But prescriptivist accounts of language fly out the window the moment you actually look at human language as a natural phenomenon. Just as the thunderbolts of Zeus turned into electrical imbalances between the ground and atmosphere, dangling modifier and double negatives turn into simple sentences perfectly comprehensible to speakers of the relevant language. If one speaker says something and another understands the utterance, then grammatically correct linguistic exchange has transpired, regardless of whether any English Grammar Rule Book rules were violated. By way of example, I ended an above sentence with the phrase, "which side of the road they drive on." Nothing exploded. No hair-pulling confusion resulted. Yet I violated a rule of "proper English grammar". But this post isn't about convincing people that prescriptivism is wrong — only that it shares a certain key feature with mysticism.
I insist that in both the case of the mystic and the prescriptivist, there is either a lack of competence in understanding the rules by which nature operates or an emotional attachment to the social implications of the rule set. The mystic cannot grasp the science behind evolution, quantum mechanics, or cosmology, much as the prescriptivist cannot grasp the science behind linguistic universals, childhood language acquisition, or sociolinguistic discrimination. The mystic feels that they are saved and loved and special, much as the prescriptivist feels that they are proper, correct, and supremely literate. But both case are driven by either ignorance or contempt. In neither case is one able to recognize the elitism involved. Or, if the elitism is recognized, it's immediately defended as good and justified. One must be a speaker of "good English" much as one must be a "good Christian". And failing to be so means that you are inferior to the defender of this (dubious) Good.
But because linguistics is a young field which has not yet permeated the cultural fabric, we scoff at linguistic discrimination just as readily as we decry racial or religious discrimination. If you can't talk good, you must be stupid and inferior to all of us who can speak well. This, however, is just ignorance of the way in which people learn language and the way in which language changes, and an almost-mystical assumption about the existence of some Platonic True Form of a given language. It is ignorance of the fact that this Platonic language almost always coincides with the way the elite speak, be they London aristocracy (where "standard" British English comes from) or Muscovite czars (where "standard" Russian comes from).
As an aside, it must be pointed out that this ignorance costs people in very real ways. Being a speaker of a non-standard dialect cannot, on principle, relate in any way to intelligence or ability. There are astrophysicists in Memphis, Manchester and Mumbai alike, each speaking very different versions of English. Sounding Black on the phone is often a sure-fire way of not getting past a first interview. Having a Queens accent is just the same. Yet such linguistic variations have nothing to do with intelligence, training, education, personability. They are merely artifacts of our physicality, of our vulnerability to our social environments as children. We speak the way the people around us speak.
A final thought: there are good reasons to have arbitrary rules. And this applies to grammatical rules. Writing is a suboptimal translation of language, because it misses so many of the nuances essential to conveying understanding, such as tone, pace, volume, expression, etc. So in order to make writing understandable to others, it is important to have usage and spelling rules. In a written document, double negatives are recognized as negating each other, rather than the sentence as a whole (as is the case in, for example, Italian). Standardized spelling and punctuation are essential to the way English is written and read. But insisting that such rules be transferred from the page to the spoken word is ludicrous. Writing is the only place that needs the extra stringency of arbitrary grammatical rules. And it inherits this property from the already-natural-rule-governed richness of spoken language.