The problem is that if the language, written or spoken, is (almost) unintelligible to the reader or listener, then the reader or listener is simply going to switch off and ignore the writer or speaker. Which may well be a disadvantage to either person, or even to both people. Furthermore, it can lead to negative feelings in either direction.
Posts such as that above by Ady1 do not, in my opinion, add anything, rather they, by making fun of the problem, they trivialise what is a serious problem to some people.
I fully agree with Bodger Brian about the unintelligibility of posts written as he describes. Unfortunately, this isn't a problem just on this forum as it happens elsewhere as well. And I don't think misplaced or missing commas is the reason either: it is a specific lack of understanding of even the most basic rules of grammar, something which has been getting worse since certain people decided that ideas communication was more important than knowing the basic rules of grammar with which to communicate those ideas. It seems to me that the quote by Hopper immediately above is an example of this, in my view, misplaced thinking – and I don't care just how much his professor knows – intelligibility has to be important.
I am well aware that some people appear to use a different form of English to me – I'm thinking of those people who use words such as "yous", or as a 13 year old boy said to me when describing toothache: "It's painin' us!". But at least it was readily decipherable and hence easily understandable. But there does appear to be a group of people to whom the basics of grammar, and sentence construction is an alien concept.
I have no experience of tablets, smart-phones, or other electronic devices other than my computer, yet I cannot see that it is not possible to correct something after insertion into the forum: there is, after all, an edit function available within the forum. Therefore, I don't necessarily agree that the problem is predictive software – unless the problem is actually that the writer cannot see the layout after insertion.
What the answer is, I really do not know, other than a return to old-fashioned methods of teaching grammar, but that won't go down too well.
I'll leave you with a saying I've heard a few times: "If you know how to spell, then you are over the age of 50 (and hence subjected to the old-fashioned way of being taught English)". And yes, I know I've introduced a new factor, but it's all part of the same problem.
Regards,
Peter G. Shaw
(who, by the way, failed English Language, English Literature and French at GCE 'O' level, and dropped Latin after two years).