I listened to this course by John McWhorter from The Teaching Company for the second time while on my trip to Ohio and back. It goes 18 hours, but he is an excellent speaker, so I found I could go hour after hour with him. Many libraries carry the course, if you want to pick it up.
He spends a lot of time explaining what language is, how it changes, how many there are and what types before he gets into the controversial stuff. I think that is wise, because there is a lot that needs to be understood about languages, dialects, and creoles around the world before getting into the controversies of Black English.
Which is why I'm going to ignore that and just tell you stuff.
None of us speaks standard written formal English at home or with friends. I come much closer than almost anyone, because I took that on as an affectation quite early in life and much of it has stuck. Yet even I am not all that close. I also make my writing more colloquial than most formal writers would, to bring it more in line with how I speak. Punctuation, in particular is more impressionistic than formally accurate in my writing, creating pauses, changes of tone, and changes of voice as if I were reading aloud. Still, recordings of my conversation are not very close to my written expression. McWhorter gives examples of words that are almost never used in speech but are common in writing, such as "refreshing." I might say the word "refreshing" with an ironic tone - say, after vomiting. I might say "When will you arrive?" in a semi-ironic tone or to quickly escape from a double-entendre that some of my knuckleheaded friends might jump on.* But really...generally...no. Arrival is a written, not a spoken word.
It is mostly a social advantage to come from a home-dialect that is closer to written standard English. People think you are smarter, more conscientious, better educated when you are speaking naturally. However, there are also social situations where you will seem pretentious and artificial if your speech is too close to written standard. You could get beat up, actually, which most of us consider a serious disadvantage. Everyone in America - everyone in any language, actually - has command of a continuum of speech from home-dialect to formal.
Black English is not the only dialect looked down upon. Most Southern dialects are looked at askance (looked askance at?), though the accent can be used to good effect formally. Entertainers and politicians (but I repeat myself) use dialects with skill by adjusting the blackness, southernness, Brooklynness, Jewishness, academe, or hispanicness of speech to win others over. It is usually more natural than calculated.
Having command of only the home-dialect, as many urban African-Americans have a command of Black English without much extension into written standard, is a significant disadvantage. This is true not only in America, but everywhere in the world. There is a prestige dialect which gor to call the shots about what the written standard would be, in Paris, in Asuncion, in Jakarta. In some countries, such as Germany, various regions each have enough juice that they don't always regard other dialects as inferior, just different, but that isn't common.
So McWhorter is not at all in favor of not pounding as much written standard English (and the general American English spoken dialects) into urban black children, same as rural white children or suburban Asian children. He thinks it is necessary for anyone who has aspirations for life outside one's own community. But he is very clear, as linguists generally are, that Black English is no worse a dialect than any other. It is not degraded English. The verb tenses - She be walking - are taken from Celtic forms, mostly Irish and Cornish. Think Pirate Talk. Arrggh. They have their own nuances and distinctions. It's not a creole, unless you want to say it's a hemisemidemi creole.
All mother-dialects are nonstandard compared to written standard, but not sub-standard, because they are oral language, and none is inherently better than any other, though we feel differently about them because of how they fall on our ear. BTW, oral language is real language to most linguists. There are about 6000 languages and only 200 are written, and that is all very recent. The written inscriptions and even the texts from the earliest days of writing are very artificial by design. They use language - real language, which is oral - to set something down in record. When the OT records spoken word it is usually stylised court-language or legal language, or storytelling, as in Job or Genesis. The NT is closer to our own idea, but still not very close. Jesus reports a conversation with Satan in a few sentences that covers 40 days of spiritual warfare. I'm betting that getting the quotes right wasn't as important as hammering the key points into us. Real spoken sentences leak out, often amusingly, but weren't the norm. The HT writers were often making declarations, not recording dialogue.
That African-American Vernacular English (to use its other name) sounds less educated and less-standard is a result of history, and the past isn't going away. But we don't have to perpetuate it, and we certainly don't have to make it worse by treating it as substandard.
*"Know your audience,"the first rule of public speaking.