I am 42 and went to school in the 70/80s and I don’t remember being taught grammar very much or other details of the English language. I’m not sure what an adverb is for example and I don't know which is correct out of compared to and compared with. Maybe SPaG of this type of out of fashion at that time. We also lost a lot of teaching time due to strikes.
However, I now have a first class scientific degree, professional qualifications and work in a professional job that requires written work and I read a lot for pleasure, so I like to think I have a reasonable standard of written English.
However, I know that lots of people have not had such an education, do not need to write much at work, or have other issues such as English not being their first language, or SNs like dyslexia. I also don’t think internet forums, or facebook etc require perfect written English and while it is nice that the standard on MN is very good, it is not compulsory and I don’t think it is acceptable to pull others up on their mistakes.
No-one knows who the person behind the post is and it is not on to comment on their written English in an informal setting. It is especially hypocritical on here, where almost any other kind of judging is mercilessly jumped on.