Good grammar shows care was taken in the response

The argument

In writing that is meant to be referenced again and again, good grammar matters and shows care was taken in the writing. Think of a doctor or scientist. We expect them to have a well thought out position, that is clear. The expectation is not merely aesthetic: a reader who cannot check the writer's reasoning directly has to judge it by what is visible on the page, and the care taken over the sentences is the available evidence of the care taken over the thinking. Grammar also bears on whether the message survives transmission at all. Just as an improperly configured telephone wire can cause static during a phone conversation, improper grammar can likewise affect the meaning and clarity of an intended message. Writers should be professional by having correct grammar, because the alternative degrades the signal rather than merely decorating it poorly. Some common errors are with sentence structure, subject/verb tense, punctuation, spelling, and other basic mechanics and parts of speech. The consequences are not proportional to the size of the error. Even something as simple as a misplaced comma can completely change the meaning of a sentence. For example: "Let's eat Grandpa." vs. "Let's eat, Grandpa." A single mark determines which of two entirely different sentences the reader receives, and nothing else in the sentence corrects the mistake. There is a cost to the reader even where the meaning does come through. Grammar makes written content more readable and in turn more interesting. If it is necessary to repeatedly reword sentences while reading, the flow becomes disrupted and involvement in the story halted — attention that should go to the content is spent repairing the prose instead. Therefore, grammar lays the groundwork for effective communication.

Premises

Counter-arguments

Two different things are run together here. Every variety of a language has a grammar — regional and social dialects are rule-governed systems, not degraded versions of a standard. What the entry calls improper grammar is generally divergence from one prestige variety that acquired institutional backing through schooling, publishing and administration. That is a social convention, and a useful one, but it is not the same as the machinery that makes communication possible. The consequence is that judgements of care and professionalism attach to a dialect, which is how grammar assessment becomes a proxy for class, schooling, region and whether a writer learned the language as a second one. Several of the examples are not grammar at all. Spelling and punctuation are orthographic conventions; the comma in the stock example is a typographic mark standing in for an intonational pause that no speaker would omit. That example circulates so widely precisely because genuine cases where punctuation destroys meaning are hard to find — in real use, context resolves the ambiguity instantly. The readability claim is empirical and only partly supported. Readers recover intended meaning through substantial non-standard usage with little measurable cost, which suggests the real function of the conventions is the signal they send about the writer rather than the comprehension they enable. The rival position grants that signal matters in formal registers while denying that it makes grammar matter in the way claimed.

Rejecting the premises

Good grammar could be used by bad actors to make a poor argument seem more official.

Framing

This is not to say poor grammar is unreliable or not well thought out. It’s a courtesy to the reader. There are plenty of writing checking tools that can help polish writing.