Are we assuming that all bad spelling is the result of dyslexia, though? None of the many spelling errors we see all the time are made by anybody without dyslexia? Obviously, there will be typos and stupid autocorrects, but IF it wasn't done by mistake/because of dyslexia and comes from a point of ignorance, would you not want to learn? How is it particularly different from any other error, really?
Just supposing I were to go off on a rant about the USA's reaction to Russia's actions and demand that Trump should put his foot down and start acting like a real leader, I would want people to point out that one particular area of my knowledge that's clearly not correct - better to be embarrassed briefly than allowed to continue indefinitely, IF it were something that I could easily learn and remember.
It's great to be kind and nobody likes a bully, but if we get to a point where people never feel able to gently point something out, everybody else sees the incorrect version and many will subconsciously absorb it as if it must/might be correct. The end result is all of the 'should ofs' and the like becoming de facto accepted as 'correct'.
Whatever the reasons behind it, if a post is full of spelling errors - maybe grammar and punctuation errors too, as well as one massive unseparated paragraph, I will often find it just too incoherent to understand and have to give up. I'm not claiming that the odd error/typo will render it thus, but would people really not want to know that, having posted something and earnestly awaiting responses and engagement, they aren't likely to get anything - not because nobody likes them or is interested in the subject, but because they've just communicated in such a way that they effectively haven't really posted at all?