Every English student knowing enough to post a question on this site understands English capitalization and basic punctuation. Why, then, do we constantly chastise people about things they already know? I'm just wondering why we can't calm down on here.
Sheer snootitude perhaps?
The word denotes a well-informed language-lover and word connoisseur. It aptly captures the linguistic snootiness of those who weigh their words, value verbal nuances, resist the societal tendency to blur useful distinctions, reject newfangled usages without strong redeeming qualities, and concern themselves with linguistic tradition and continuity.
"There are lots of epithets for people like this — Grammar Nazis, Usage Nerds, Syntax Snobs, the Language Police. The term I was raised with is 'SNOOT.' The word might be slightly self-mocking, but those other terms are outright dysphemisms. A SNOOT can be defined as somebody who knows what 'dysphemism' means and doesn't mind letting you know it. . . . A fellow SNOOT I know likes to say that listening to most people’s English feels like watching somebody use a Stradivarius to pound nails." (Wallace, "Tense Present," Harper’s, Apr. 2001, at 39, 41.)
I won't deny I sometimes get irritated simply because I'm a grumpy ole git. I certainly don't defend myself in this - in fact, I apologise for inevitable future transgressions in my ELU profile.
Having said that, as an active supporter of English Language Learners, I feel there's at least some justification for being annoyed by substandard English on ELU.
1: If the poster doesn't know any better, chances are they should be using the learners site.
2: If they do know better, they're effectively insulting the community by their insouciance.
Regardless of how it comes about, substandard English in prominent positions (questions and answers - I don't include comments in this diatribe) is a poor advert for the site. Not to mention which there's always the danger that uncorrected errors will be accepted as "valid" usages by others. For many users, at least part of the purpose of ELU is to define and promote competent use of English. Correcting or calling attention to glaring errors is obviously consistent with that aim.
TL;DR: If you don't like being picked up on grammatical/orthographic howlers, either take the trouble to avoid making them, or go to ELL (where errors are still likely to be noted & corrected, but at least no-one will disparage you for making them).