To the extent that I try to be error-free (esp. as a poet, writer, and songwriter), yes. As far as how I approach people whose grammar is horrendous, no. I advise people and help them if they need it for apps, resumes, letters, etc., but I don't criticize them harshly. Some of us are just gifted and practiced. No one is good at everything and who wants to be criticized harshly for what they're not good at?
You are right. My mother tongue is French but where I'm good at is math. My partner is good at grammar. So at home she does the letters and me the tax returns & budget :)
Otherwise I would correct yes, but always keeping in mind that a bad reasoning expressed in a perfect spelling and grammar is still a bad reasoning.
While grammar and spelling are important, the content is equally if not more important.
And true, but I'm also a hypocrite and far too lazy to write full sentences when a fragment will convey the desired message.