Anyone can learn the technical aspects of writing (grammar, punctuation, etc.) and anyone who wants to be taken seriously must.
I taught writing for years. I still make mistakes. I consider my readers proofreaders of last resort. If they point out an error, I say thank you and fix it.
But that’s different from being the Grammar Gestapo. Pointing out an error just to appear superior and slap someone down is wrong. Worse, it is impolite and uncivil.
Learn, do your best, and move along. :)