ok, so people want to correct other people's spelling and grammar. Fine. Except stop being so bloody disingenuous about it. Let's be honest here, you're not correcting spelling and grammar because you think that they might appreciate the correction/should aspire to do better/perhaps didn't know that they had got it wrong/. You correct their spelling and grammar because it annoys you personally.
I hate text speak. And I mean really hate it, and yes, I think it shows a lack of inteligence and that actually, there is no reason in the world to use it. But that is about my personal view, not about wanting someone else to better themselves, because reality is they probably don't care.
On the whole I am anal about writing. In fact I am currently writing this on my phone, but with a bluetooth keyboard so I can write more. 
However, I am VI, and as such I learned to read braille at an early age. And braille is contracted in order to make it less bulky. As such, from the age of seven I never saw a word written out in its whole form. With the invention of computers so also came the invention of the screenreader. And when you are reading with a screenreader you read down a line at a time, so e.g. I will scroll to a line in a post and it will read it for me as a sentence, not letter for letter. As such I also don't see words written out unless I actively look for them. And the other thing about screenreaders is that they don't necessarily pronounce misspelled words in such a way that you would know that they were misspelled, iyswim. Sometimes they do, if your post contains typo's I will most likely notice them. Sometimes if a word contains a double letter and you have a single one, it will mispronounce the word, and if you leave out punctuation then it reads as one continuous string of text with no spaces which is highly irritating. But words like there and their, or know and no are pronounced exactly the same. Now I am also a bit of a grammar pedant and as such I know full well the difference between know and no, but someone else might not know, because they have never seen the words written out in full, for instance.
And most importantly, this is an internet forum, it is not a professional platform where spelling and grammar really makes a difference. I am currently in the process of looking for jobs, and I am constantly horrified at the number of job adverts that are full of spelling mistakes and typo's. And believe me, if I can see them with a screenreader then they must be bad. 
and the worst of it is that these job adverts call for good written communication skills... now there is an area which needs some serious pedantry throwing in its direction. But to expect people to put in serious effort to reply on what is basically a means for people to kill time? get real.
People occasionally pull me up on my spelling. Now I don't mind if it's a genuine error which is obvious, but otherwise it says far more about them than it does me. I remember years ago writing a very long and thought out response to a post in relationships where an op was considering terminating a pregnancy, something which was highly emotive. And the next response was from theDevilWearsPrimark correcting one word in my post (of several paragraphs) which I had misspelled. 
And yes, I can name her because it turned out she was a long-standing troll.
It's simple really. if a post is so full of mistakes that it either triggers your pedant alarm or is unreadable then don't read it. There are millions of other threads here to read, and if the poster needs genuine help, then your pedantry is not going to make them feel better is it?