Online, discussions of grammar tend to display confusion about what the subject is, and the usual admixture of rubbish and emotion does not help.
There is, of course, the confusion between grammar as grammarians and linguists discuss it technically, and spelling and punctuation. But other, unstated meanings are often involved.
A post by Lucy Ferriss at Lingua Franca, "Grammar: The Movie," identifies some of the additional meanings that surface in a new documentary.
Spelling errors: If you write it's for its in your cover letter or resume, or confuse there/their/they're, you're probably not going to get the job. But these are merely spelling errors, as likely the result of carelessness as ignorance. Of course, they're obvious, so easy to spot that even a manager can see them, but they are still trivial.
Bad writing: Lord knows there is plenty of slack, inexpert, and impenetrable writing to be found, but that is not a problem for grammarians to address. Academic writing, for example, is notoriously wordy and opaque, but it is usually grammatical.
Pedagogy: The complaint that grammar is not much taught in the schools any longer is true, but the teaching was not all that effective when it did occur. The traditional schoolroom grammar is a jury-rigged structure of terms borrowed from the classical languages combined with oversimplifications, and the analytical English grammar that linguists have developed over the past few decades is virtually unknown outside linguistic circles.
In the three weeks that I can afford to spend on grammar and usage in my editing class, I rely on the traditional terminology, because scraps of that are what my students know. They would choke on the Pullum-Huddleston Student's Introduction to English Grammar, even assuming that I had the time to spend on it.
(If there is effective pedagogy out there, perhaps in ESL texts, let me know.)
Standard vs. non-standard English: Many people make the mistake of concluding that standard written English is correct English, all other variants being ungrammatical. That's just not so. We don't go in for double negation in standard English today, for example, but it was common, understood, and grammatical for Chaucer. And if someone says, "It don't make me no never mind," I comprehend immediately that the negatives intensify, without having to count them to see whether the result is positive or negative.
It would be helpful for people to acknowledge the whole range of registers in modern English, gauging which is appropriate for speaker/writer, subject, and audience, rather than declaring variants wrong.
Literacy: The standard/non-standard issue points to the cultural and political attitudes that are almost always present but seldom articulated.
Take, for example, the recent Gawker contest to determine "America's Ugliest Accent." At Slate,Josef Fruehwald exposes the underlying ugliness: The disdained accents are usually those of less-educated, working-class people. "And of course, that's what linguistic discrimination is really about. Maybe it's not always about class, but it's never really about language. It's about the kind of people who speak it. Predictably, the kinds of accents and languages which get dumped on the most, and get branded the 'ugliest,' always wind up being spoken by socially disadvantaged people."
(And by the way, Gawker, how could you have left out an accent that has been universally mocked and disparaged for decades, the accent of my people, Appalachians?)
I suppose that my having mastered standard written American English puts me in an elite class. It is a skill not easily acquired. But there is something offensive to wield that skill as a club to attack people who have not acquired it.
Turn that peever rock over, and you will almost always find snobbery and status anxiety. The peeververein will not state that openly, which is why you need to be alert for it.
Correction: Confusion over the screen image at Slate led me to attribute the article about Gawker to Dayna Evans instead of Josef Fruehwald.
I apologize for the error.