> I take issue with being held to a standard of somehow needing to "know" that ahead of time
I agree that this would be an unreasonable standard. But I've yet to see that standard being applied to anyone (And I run in circles where I'm exposed to quite a bit of very outspoken trans/nonbinary rhetoric).
What I see, time and time again, is people who explicitly refuse to call someone by their preferred pronoun, whether it's on the grounds of pure petulance ("You can't make me!"), or of some biological essentialism ("HE, because Y chromosome").
So unless you have any examples of people being attacked for a single, innocent mistake, I'm inclined to see this as a strawman (straw-person?) argument.