There is little excuse for spelling errors in this age of spell checking programs, (except for those who actually don't KNOW the difference between 'there', 'their' and they're' and related words).
But when a person, no matter how much information they have or how well they understand a subject, cannot impart that information coherently to others, there will always be a problem! Correct punctuation and sentence structure are some of the major ways we make thoughts clear and useful. I suppose that, if a person in certain situations has an editor to translate their written meanderings, it can be tolerable - but I have seen practically incoherent pages presented as finsihed products - and had to grade many when I was a graduate teaching assistant years ago.

There ARE ways to explain why grammar, punctuation and sentence structure (and, of course spelling) make communication easier, but if not done early on, it is difficult to 'fix' later.