I Won’t Hire People Who Use Poor Grammar. Here’s Why
hbr.org
hbr.org
That said, I used feel the same way. I excelled at writing when I was a kid and was always super judgmental of those that made grammatical errors, even online. I'm not sure if it was getting older or what, but I started recognizing that I'd make the very same grammatical mistakes that I'd judge others about from time to time.
I don't think all grammatical mistakes are created equal, and the context and audience of the content in question really matters. Poor grammar in marketing material that world will see is really bad. Making a grammatical error while trying to urgently respond to an issue in an internal slack channel is not a big deal. Context really matters.
I agree with the article that you need to make an exception for people with English as a second language for spelling and grammar... but you should not make that exception for the clear expression of ideas.