What exactly separates the grammar of "I (and Dave) am going" vs "Dave (and I) is going"?
The same thing that seperates the first one from "going Dave am I and". Word order matters.
the order of the coordinations is a matter of style, not grammar.
Categorically false
Therefore, the only "wrong" grammar is constructions that natives wouldn't use
Wrong again. Plenty of native speakers of just about every single language there is have atrocious grammar. Native ≠ correct grammar.
It's not wrong, merely a different register of speaking
It's wrong when it comes to grammar. Whether or not gramatically incorrect colloquial speech is acceptable and sometimes even preferable to being gramatically correct (it is in most cases, but in some it can be very grating) is a different matter entirely.
Accepting only prestige dialects as "correct" grammar
Nobody said anything about dialect
people continue to think things like "black people don't speak right
As I mentioned earlier, colloquial speech can be as good as or better than gramatically correct speech in some cases.
You're mixing up a whole lot of things that aren't grammar and just generally being wildly wrong all over the place.
Just because there is no central authority does not mean there is no general consensus. English classes from elementary school to university aren't accidentally in line with each other by some weird coincidence.
Descriptivism has a place in the evolution of language, but not in a wholesale "everything native speakers might say is grammatically correct if they are understood".
English classes from elementary school to university aren’t accidentally in line with each other by some weird coincidence.
So who has the authority when experts disagree? Like I said, no one is saying "I house go" but some people think "Give this to whomever comes here first" is correct while others argue for "whoever". Descriptivism by definition seeks to explain how language functions. Prescriptivism only works within a narrowly defined framework, like APA or MLA for example, but even within those there's disagreement.
The same thing that seperates the first one from "going Dave am I and". Word order matters.
Categorically false
Wrong again. Plenty of native speakers of just about every single language there is have atrocious grammar. Native ≠ correct grammar.
It's wrong when it comes to grammar. Whether or not gramatically incorrect colloquial speech is acceptable and sometimes even preferable to being gramatically correct (it is in most cases, but in some it can be very grating) is a different matter entirely.
Nobody said anything about dialect
As I mentioned earlier, colloquial speech can be as good as or better than gramatically correct speech in some cases.
You're mixing up a whole lot of things that aren't grammar and just generally being wildly wrong all over the place.
Then who's the authority on grammar? We don't have a single entity like the academie francaise.
https://en.wikipedia.org/wiki/Acad%C3%A9mie_fran%C3%A7aise?useskin=vector
Just because there is no central authority does not mean there is no general consensus. English classes from elementary school to university aren't accidentally in line with each other by some weird coincidence.
Descriptivism has a place in the evolution of language, but not in a wholesale "everything native speakers might say is grammatically correct if they are understood".
So who has the authority when experts disagree? Like I said, no one is saying "I house go" but some people think "Give this to whomever comes here first" is correct while others argue for "whoever". Descriptivism by definition seeks to explain how language functions. Prescriptivism only works within a narrowly defined framework, like APA or MLA for example, but even within those there's disagreement.