Chandra, a "recovering grammar snob" who works as an English teacher, has a smashing trio of essays on Literacy Privilege — the invisible privilege that accrues to people who have the facility to write well and clearly, and who have absorbed the "correct" conventions of English. I know I've been guilty of dismissing people because of their grammar/spelling errors (I'm sure I'll make several in this post, BTW, thanks to Muphry's Law), and I've also posted regrettable grammar-mockery in place of rebuttal at times. Even when I was doing it, I knew that it wasn't quite fair or rigorous but Chandra's critique is a good frame for understanding precisely what's wrong with the practice.
One important issue that Chandra doesn't touch on in her essays is the way that this works in languages where an official academy defines formal correctness — French and German, for example. English is very much up for grabs, thanks to the absence of any final authority over its rules. In other cases, there is a technically correct way of doing things, and an incorrect way — presumably, this exacerbates the problem.
Literacy Privilege Checklist:
I can easily and safely navigate my way around the city I live in because I understand all of the posted signs, warnings and notifications.
I can make healthy and informed choices about the products I purchase because I can accurately read their labels and price tags.
I can safely use pharmaceuticals prescribed to me without having to remember the doctor's or pharmacist's instructions because I can accurately read their labels.
When required to visit doctors, hospitals, government agencies, banks, or legal offices, I do not have to invent excuses to bring paperwork home so that someone else can read it to me. If I live alone, I do not have to expose myself to judgement and ridicule by asking the doctor, nurse, agent, clerk, lawyer or other employee to read it to me.
I can independently make informed medical, legal, political and financial decisions about myself and my family because I can read and understand important documents.
I can be sure that my paycheques and bills are accurate because I can read them to check for errors.
I can acquire a driver's license and its associated freedoms because I am able to complete the written test for a learner's permit.
I can accept invitations to a restaurant without anxiety because I know I will be able to read the menu.
I liked this bit from her FAQ:
2. But people who write professionally for a living – journalists, authors, researchers, pundits, etc. – should surely be held to a higher standard than the rest of us!
2(b). Oh. So it's okay to go all apeshit caps-locky self-righteous grammar-banshee on their ass when I see a mistake in one of their articles?
I am not able to grant or withhold permission for anyone to be a douche to anyone else. That is not my purpose here. I simply encourage a more compassionate and respectful approach in these situations.
Think of how many thousands of words a professional writer writes. What percentage of those words involves spelling or grammar errors? Probably a very small percentage. Professional writers are also human beings, and sometimes they slip up, or sometimes they have learned different rules than the ones you've learned. Correct them if it makes you feel better about the future of humanity, but maybe try to do so in a way that does not encourage brutal verbal abuse against all people who can't spell.
Man, is this ever on the money. I've had people send me the most amazing, over-the-top, dramatic denunciations because I used grammar they didn't understand (UK usage, for example); presented fictional characters whose speech was colloquial (dialogue is privileged); or violated an imaginary grammar rule (for example, the made up prohibition on "double negatives"); or just made a typo (I type all day, and some of my keystrokes will be erroneous).
It's one thing to point out a typo, it's another thing to denounce its creator as an enemy of literacy and a bad example who will lead the children of the world to ruin.