Made a good living translating between english, redneck and sometimes ebonics from professionals to trades people. You make your language fit your audience if you want to accomplish something. In fact I would say it has been my major skill in business.
I agree with this to some extent. I have family in the corn belt and when I am around them, I find my self slipping back into the accent a little more and using some of the dialect. It's one thing for it to be sort of a natural transition but it sounds terrible when it is forced. Think about a radio ad trying to sell something to a rural audience and the announcer puts on a faux southern accent. It sounds cheesy. Same thing with Joe Whiteguy copy trying to break out the ebonics.
I think it's interesting to study accents and dialects but that is completely different from just being wrong if we're talking about a semi-formal setting. Words mean things and if you want to communicate well and be convincing, you need to use the right ones. It's one thing to be slightly off on a nitpicky Grammar Nazi point but it's completely different to fail on basic vocabulary. Nothing I posted, at least, is what I would consider Grammar Nazi.