Too often, I think, this kind of thing becomes a way to separate people, and can overtake the underlying ideas. Absolutely. I say that above. Grammar rules create a kind of elitism to keep the Barbarians out of the academy.
We agree more than we disagree. I don't care for arbitrary rules. Some rules are arbitrary. Spelling "correctness" is usually a process of evolution. One year "e-mail" is hyphenated, according to the dictionary. By the second edition, the hyphen is gone. When Wired Magazine unilaterally dropped the capital on Internet, that was good enough for me. Who is the emperor? Is it Wired?
Which rules are arbitrary and which have evolved to build clarity? You will understand both neighbour and neighbor. Do you think I should use both in a single paragraph? It's pretty arbitrary that we choose one or the other spelling? Should I bother pointing out to my student that he used both spellings in one paragraph?
Also you are right about my use of the word "correct." I was wrong to use that word. Even works that seem "concise" and "unambiguous" to me may not be so to you.
Rather than "correct," I should say, "generally accepted by the authorities" currently claiming responsibility for Canadian English. That is not me. We do however have an Empress of Canadian English: Katherine Barber. I refer students to two books considered authoritative by publishers, newspapers, and the government of Canada. These are the Oxford Canadian Dictionary and the The Oxford Guide to Canadian English Usage.
When I'm confused by someone's writing, I let them know. They should consider the reader.
If they want to know what is currently considered "correct," I will relay the opinion of the authorities. Unfortunately, it is often the case that those who will give you money for writing a research proposal (Mitacs, NSERC, SSHRCC) will want you to follow arbitrary rules of "correctness." Do you think students should know those rules? What do you think?
I still think the more you perfect the style, the more you perfect the message. (And the more you perfect the message, the more you are perfecting the style of delivering that message.)