Re 'My unicorn don't like your unicorn' and
Congratulations your engaged' - and their comments, IMO the thing is that people who blithely make these mistakes obviously can't see anything wrong so have no idea of how they make other people wince. So from their POV, what's the big deal?
I had a writer friend whose novel was accepted at the same time as mine. She had the ideas, but her grammar and spelling were appalling - basic mistakes on just about every other line.
The freelance copy editor who had to sort it out told the chief ed. that she'd want double pay for any more by that author. As a consequence, friend was told to have any future novel professionally copy-edited before submitting it.
I did try to help her. She wasn't actually dyslexic or lacking in intelligence - it was mostly the endless confusion of its/it's, who's/whose, your/you're, lose/loose, there/their/they're, etc. But I think she had a mental block about it. Although I told her these things were very simple if explained properly, as I was quite prepared to do, she'd made up her mind that it was all too difficult, it was beyond her, so she wasn't even going to try.