Double negative makes positive?

Leaving aside the topic of whether or not the way we use language has social implications (i suspect most linguists would say usage does have social implications), i'd point out to you that what so many English speakers see as "logic" in the use of negatives ain't necessarily so.

In many languages, not only are multiple negatives common, they are required. In English, one might say: "I don't eat apples, or pears or peaches."--one negative. In French, one would say: "Je ne mange pas de pommes, ni poires, ni pêches.--that's three negatives. The word "ne" negates the verb, the word "ni" (which would translate as "nor") is then required in the seriation, because French grammar requires multiple negation so that there is "agreement" about the negation. One might also say: "Je n'ai aucune idée." A reasonable English translation would be "I don't have the slightest idea." But actually, it literally says: "I don't have no idea."--again, the negative is multiplied by the rules of grammar.

Before you say, eh, French, so what? I'd point out that multiple negatives were common in English until about the the time of Shakespeare. It was only early in the 17th Century that grammarians in English began to say that multiple negatives are not "logical." Even then, it took many decades before the rule took over in literate circles, and the "common" people continued to use multiple negatives. When the English colonies on the North American continent began to be settled, most commoners still spoke English as it had been spoken in Elizabethan times. So, for such a person to say: "I ain't got no apples."--was considered perfectly reasonable by most of his or her fellows. It was the well-educated classes who would have looked down upon such usage.

And there you have an example of usage having an effect on social perceptions. People who used multiple negatives did so simply because that was how they had learned the language. But others among English-speakers, who had been formally educated, and who had learned the new rule about the "logic" of negatives, could employ that usage as a measure of the literacy and education of the speaker.

It's rather like addition versus multiplication: some languages employ the logic of addition (a negative + a negative = more negative) while some employ the logic of multiplication (a negative x a negative = a positive). Of course, a portion of the English-speaking population has always spoken "nonstandard" English (regardless of which English), so this probably doesn't mean that the grammatical expertise of the population is decreasing.

Of course, one must also account for dialectical appropriateness. As an English teacher, I'm expected to use "standard" English in the course of my job (though the efforts to maintain a standardized form of the language has stymied the natural evolution of the language), but it would be unnatural and inappropriate to employ that dialect rather than the regional dialect I was raised speaking while visiting my family back in Michigan's Upper Peninsula.