But I'm confused by your sentence regardless of the gender terms. Did they notice the tomatoes in the Garden or in the greenhouse? This is just ambiguous wording in general.

- These are two different sentences, but they're separated with a comma. It should be a period, as it makes no grammatical sense with a comma unless you're trying to make it intentionally confusing.

- You would write "They both went into the greenhouse" if they both entered, or you would write "Y entered the greenhouse and noticed the ripe tomatoes."

- "Before entering the greenhouse, "Y"/"they both" noticed the ripe tomatoes in the Garden."

It was used whenever gender was ambiguous or needed to be protected. Now with people openly identifying as non-binary, there is not a more specific pronoun, that person doesn't consider themselves that gender. You would be referring to them as something that is not what they want to be called, and is not what their social circle refers to them as. It's confusing, especially if you know what to call them but choose not to because you're offended.

> I don't think it's unfair characterize this as an offensive move, waged by one side in a 'culture war', that was done without regard to collateral damage

I would wager, based on the disproportionate and melodramatic language, this has never actually affected you. But you are likely consuming media that tells you everyone is going to draw and quarter you if you mess up a pronoun. This is not the case. Trans people just move on, they're used to it. It literally happens all the time.