Those "rules of grammar" you're citing have been defined by a very specific class (and frankly, color) of people, and then dictated to students.

Language is functional when it communicates ideas sufficiently from a speaker to their selected audience, and it's the speaker and their audience who decide that.

With regard to the specific sentence "I didn't do nothing," ~~you wouldn't have asked this question if you didn't already know what such a speaker was actually trying to communicate. You just don't like it, and that's a you thing.~~

Gah - just realized you're not OP. My previous paragraph still generally stands.

I made no such racist argument and for you to suggest that I’m racist merely because I pointed out that grammatical rules have purpose and utility simply demonstrates how little you understand the historical context you’re trying to weaponize and how eager you are to slander those who disagree with you as racist. You’re not winning yourself any real points for combatting racism, you’re just exposing yourself as an empty virtue signaler.

First off. lets look at people who have, historically espoused the idea that double negatives are "illogical" and "ungrammatical.

Robert Lowth, for example, was a Bishop of Oxford; and leader in the Church of England. Raging classist. who liked to cite the use of double negatives as a reason for why commoners were stupid.

Lindley Murray, He was a Quaker, a Lawyer, and Loyalist during the American revolution whose loyalties were likely tied to protecting his wealth, which came from his father's shipping company. His prescriptive rules as for English Grammar was oft cited as an example of "poor" education, and his rules were focused on emulating "the best writers"... which were universally rich nobles. Murray's rules were not based on common use, but rather the use by a specific subset of predominately white elites.

Both Murray and Lowth were members of those elites, and contributed significantly to perceptions that not speaking as they had was a sign of poor education and poor upbringing. They believed it was so largely because that's how they themselves spoke and wrote . That perception was taken to it's extreme in defending slavery, arguing that, for example, slaves and their descendants were inferior- or inhuman- because of how they spoke.

I cannot say if you are racist. I don't know you. I can say, however, that the most-often cited proponents of double negatives being bad grammar were straight up assholes. I generally assume that most people don't know that. But that brings me back to what I've been trying to say this entire time: Prescriptive Grammar assumes that a specific way of speaking or writing is somehow correct, and all others are, if not outright wrong, then inferior. And that is blatantly untrue.