What should we use as gender-neutral pronouns for non-binary people?

Many already accept they/they as proper grammar

Question: What should we use as gender-neutral pronouns for non-binary people?
Position1 of 3›: We should use the already-familiar "they/them" as a gender-neutral pronoun for non-binary persons
Argument‹2 of 2: Many already accept they/they as proper grammar

In today's society where the LGBTQ community is starting to receive recognition, many English teachers have already adapted and allowed their students to use they/them as gender-neutral pronouns.

The argument

A majority of today's teachers and grammarians are beginning to accept the use of singular "they/them" for persons of unknown gender and for non-binary persons. That matters because the main objection to the usage has never been about respect but about correctness — the claim that singular "they" is a grammatical error being imposed for social reasons. The people whose profession is to determine what counts as correct are settling the question in the opposite direction. Not only are teachers beginning to embrace their students' use of the singular "they/them" as gender-neutral pronouns for non-binary persons, but many are also beginning to use these pronouns for themselves. In today's society, where more and more people are coming out as non-binary, it should come as no surprise that a number of teachers have done so as well. In addition to using singular "they/them," some non-binary teachers are also adopting the honorific "Mx" to replace the gendered "Mr, Ms, and Mrs." Adoption by the people who teach the language is not a peripheral development; it is how a usage becomes standard rather than merely tolerated. The formal apparatus has followed. Teachers and students are being trained in the modern use of singular "they/them" through well-renowned scholarly websites such as Purdue OWL, which has an entire article explaining its usage as "gender-inclusive language" and highlights the reasons why students should be using gender-inclusive language in their writing. Even more notable is that the American Psychological Association has accepted singular "they/them" as proper gender-neutral pronouns — an authority on writing standards rather than on politics. The practical advantage of "they/them" over a newly coined pronoun follows from all of this. It is already in the language, already taught, and already sanctioned by the institutions that adjudicate usage, so it requires no one to learn a new word — which is why it is what we should use.

Premises

[P1]A pronoun should be adopted as gender-neutral if recognized authorities in language and education already accept it as proper grammar. [P2] Teachers, grammarians, scholarly resources like Purdue OWL, and the American Psychological Association already accept singular they/them as proper gender-neutral usage. [C] Therefore, we should use the already-familiar they/them as the gender-neutral pronoun for non-binary persons.

Counter-arguments

Many teachers are still adamant that "they/them" is strictly plural, and that its use as a singular pronoun for any reason is improper grammar.

Rejecting the premises

[Rejecting P1] Many teachers do not agree that using singular "they/them" as gender-neutral pronouns should be accepted as proper grammar.

Proponents cited

Ben Kesslen
“Luebbert is a nonbinary, 9th grade English teacher in a Philadelphia public school. Luebbert uses they/them pronouns and has their students address them with honorific Mx. — a gender-neutral alternative to the gendered Mr., Ms., Miss and Mrs. that most of us grew up using for our teachers.”
Anonymous
“One common bugbear of the grammatical nitpicker is the singular 'they.' For those who haven’t kept up, the complaint is this: the use of they as a gender-neutral pronoun (as in, “Ask each of the students what they want for lunch.”) is ungrammatical because 'they' is a plural pronoun.”
Dennis Baron
“Yes, teachers are expected to model good grammar as well as teach it—they could lose their jobs if they don't—but no matter what you’ve been told before, singular 'they' is grammatically correct, and the American Psychological Association's influential 'Publication Manual (7e)' is the latest authority to agree.”