What is it you care about, Gabriella?
The mistakes themselves, or the fact that people make them? There’s a difference.
Personally, it doesn’t bother me on an Internet forum. Anyone can post, and that’s all to the good.
But if I received an official letter, or a letter from a medical practice, say, or a solicitor with a spelling mistake it would make me wonder whether the person sending it was actually up to the job.
What does irritate me on GN are the stream of consciousness posts, without paragraphs and/or punctuation, because reading them is so laborious.