to be not only understood but thought to be a good commuinicator, you have to keep up with whatever the current rules are Rhuby
I am absolutely not going to let someone who says "ain't got no" set the standard for me; I don't care how famous they are. Jackie
What I'm really meaning is, not so much that you have to use the constructions that you dislike, but that you have to accept the obvious meaning implied by common phrases, like the one that you quote, without comment.
Like you, I would not seriously use "ain't got no" to express my lack of whatever, but when someone else uses it, I do not pretend to take it at it's grammatical face value - I understand that person to be expressing a lack.
I think most of us do that, anyway.
(Afterthought) I also mean that we should not use old and outmoded grammatical constructions to audiences who do not relate to them. I use quite high-flown language on this board, because I believe that no-one will find it too obscure (laughable, perhaps!). I also use a wide vocabulary when I'm teaching - and try to keep to the grammatical standards with which I was raised.
But I use a much more "ordinary" set of words and constructions in the pub of an evening.
