[mlyle]

> know that the candidate is a woman but still say "them"

Actually, the he or she agreeing with "them/their" later in a sentence is old and widely accepted. So a fair deal of this usage is a linguistic oddity.

> or its a person that considers herself "non-binary" and insists that you use gender neutral language.

The preferred personal pronoun thing is different. It has its own discussion and justification.

I am purely talking about "they/them" to refer to people of unknown gender, instead of "he" or "he/she"-- the singular, personal "they".

It went from occasional use in the 1300s-1600s to "wrong" in the 1800s. Now it's emerging as a best practice. Even though style guides that otherwise moved to gender neutral language in the 80's rejected it, it grew organically for quite awhile before starting to become accepted.