Too many middle and high school teachers give their students the mistaken impression that writing well means writing without errors. It is not true.

The mechanics of written language matter, and it's important to learn and practice correct spelling, grammar, and punctuation. But what matters most is to communicate your ideas, to tell your story.

When I taught Intro to Creative Writing at UCA, I rarely corrected errors of that kind. (I describe my approach here.) If a student was really having trouble with grammar etc I would refer them to the writing center for help, but my job was to introduce them to story arc, character development, point of view, figuration, voice--big picture issues. I wanted them to get the damn thing written first, then rewrite and revise until it said what they were trying to express, and only at the end go through to fix mechanical problems.

As for correcting a fellow writer on Medium, I'll send a private note sometimes, but only if the error affects the meaning and/or confuses the reader. Folks who publicly shame a writer over petty matters are IMO little more than trolls.