Once you know what they want to be called, then you (in the general sense of”you”, as I’m posting to more than just Thxone) are being a douche by calling them anything else. And you’d only be doing it to BE a douche, not because you are “old fashioned”.
Not everyone has made the choice, but it’s not their choice to make for “they”, any more than they can tell the Luddite how to live life.
An analogous perspective: I don’t get along with someone at work. I very clearly tell them to keep their distance, I keep mine, we do our jobs to the best of our ability. But…they always happen to bump into me, or make obvious gestures my way while talking to others. Then it’s a problem. They’re not respecting my choices.
Just like insisting on calling someone “she” if the preferred pronoun is “they”. It damages you in no way to respect others, yet you’ll refuse just in order to be a contrarian.
What’s the point, other than being a douche?