I think it depends on how and when people pull others up on their spelling tbh.
My spelling is crap and I am always being pulled up on it. But I do think that I can write fairly elequantly, so it does grate a little when I write out a long, considered post and someone rushes in to point out my one spelling mistake. I don't make excuses for my crap spelling, but an explanation for it is perhaps that I read braille, and from the age of seven that braille is shortened into contractions so you never see a word in its full form. Once I started using a computer I used a screenreader which speaks the words as I type them. so essentially, while I do write all the time, I never actually see a word written out in full, and so sometimes, if jaws doesn't mispronounce the word I might spell it wrong. so e.g. jaws pronounces 'racist' and 'racest' exactly the same, so if I were in doubt it would be easy to misspell it.
Same with counsellor/councillor/councellor - all pronounced exactly the same by the screenreader.
As I said it's not an excuse but it does perhaps go some way to explain.
Also I think that sometimes we lose site of the fact this is just an internet forum, and that nothing we write here is being written in professional capasity and is often written while a poster is doing something else. It is perhaps a bit unreasonable to expect that people spell/grammar check their writings before posting. I do often stick a word into word now and spell-check it before posting for fear I will incur the wrath of the pedants.
Also, I think people need to think about when they are pulling someone up on their spelling. I remember years ago I posted on a sensitive thread, the op had found out she was pregnant and her dh was pressuring her into a termination, she was very upset and lots of people gave sensitive advice. I wrote out a long post and it had one error in it, and someone came on to point out that one spelling mistake. Sensitive threads of that nature are not the time or the place to do that IMO. Also, if you are that bothered by one spelling mistake that you can seemingly overlook the nature of the thread and everything else in it but feel compelled to point out the one error, then perhaps you have bigger issues of your own that should be addressed. 
I have no tolerance for text speak though and anyone on my twitter/facebook that uses it is summarily deleted.