You have a point, Totopoly.
If I was posting and had difficulties with writing and particular with some words or dyslexic or English not being my 'mother tongue', I would say so at the start. I post on another forum where there are two people who make lots of mistakes, one has a sight problem and the other is dyslexic. Nobody criticises them because we all know about it and if a new person comes along and says, "What on earth does that mean?", another person will just say that the poster is dyslexic or whatever. Then the new person says, "Oh sorry, I didn't know", and it's not a problem.
The fact is that people who do have the difficulties outlined above and other issues, have frequently not been helped at school which is quite appalling! Some schools are very good and bend over backwards to help children who have those problems but an awful lot aren't.
I know somebody who cannot read except for a few easy words and their name and address. When he does try to write anything other than a Christmas card it's almost illegible. He has two sons, one of whom has the same problem; he was helped at school but not as much as he needed. I think adult illiterate people, if they know the alphabet and the sounds of letters, could start off writing words phonetically; shorthand is based on phonetics so it's not difficult to do and at least an illiterate person would be able to communicate. However, I'm going off the point.
Most of us have absolutely no excuse for writing ungrammatically. It's an insult to the people they are addressing. Everyone makes mistakes when they are writing but that isn't the same as a perfectly 'normal' person constantly repeating the same errors over and over. They are just lazy!