The double negative is one of those forms that many prescriptivists believe can be decried on 'logical' grounds. J.E. Metcalfe says in The right way to improve your English, "'different to' is wrong simply because it is illogical." And the argument against a double negative denying a positive uses the same appeal to logic and mathematics to say that one negative cancels out the other. So "I didn't see nothin'" 'logically' means that I did see something. This argument has been made long enough to have elicited a counter. Language isn't math. Other languages use the double negative. English previously used the double negative. People still understand the intention of the phrase, etc.
Here some prescriptivists like to bring aesthetics into their corner. In his attempt to chart the territory between descriptivism and prescriptivism, Alex Rose writes
It’s the difference between playing a scale and playing a sonata; between eating for nourishment and eating for pleasure. One way gets the job done, the other gets it done well.
Why do so many prescriptivists think descriptivists are unaware of eloquence. Is my writing plain. Is it very plain. And is it boring. Is it really boring?
So some will claim that a phrase like I don't have nothin' more to say just isn't eloquent. Or at least it doesn't communicate culture and education as well as I don't have anything more to say. Better yet would be I have nothing more to say.
I'll get to the point. Some double negative forms are marked and easily noticed even though they occur in casual standard English. These are forms that we would not expect to find in writing. Certainly not in formal writing. But some double negative forms are making their way into standard speech and even writing unnoticed. Just this morning I heard an articulate speaker on the radio say "I wouldn't be surprised if we don't find [this] out later," meaning, as I gathered from his tone and the context of his claim, that he expects that yes, we will eventually come to the realization. This is sometimes called "overnegation." It has been discussed on Language Log several times.
In one post Mark Liberman asks, "Could (some) overnegations in English be a formal residue of a stubborn hankering for negative concord?" I like the question. It's a nice retreat from his initial conclusion (oxymoron?) that this form is "not a dialect form or an idiom, it's just a mistake."
Of course the argument for a mistake based on confusion is nicely supported by the common use of multiple negation to deliberately clutter and entangle a claim or question. Now I can't remember the exact wording, but I remember the end of one episode of Cheers when Diane vowed to say "no" to any question Sam asked, and he quickly asked her if there was any way she would not object to not going to bed with him.
Where are those online scripts when you need them?
I may be trusting my ear too much here but it doesn't sound like a deliberate affectation to me. I include this example not to show that knowledgeable linguists make mistakes too. Better illustrated, I believe, is the increasing acceptability, or decreasing markedness, of double negatives in standard and even written English.
Who needs a script? I was just watching my daily dose of reruns and the episode of Cheers came on. As Diane plays coy promising to answer either 'yes' or 'no' in whatever way will reject Sam's advances he teasingly asks "Is there any way that you would not object to not going to bed with me?"
Apparently my memory's still okay.]