I would say people getting mad about a they instead of a he/she even after disclosure are being unreasonable. The word they is neutral ground in text conversation. I can see it being awkward to use in a direct conversation, but so often in threads, we're talking to the public not the individual.

Having said that, I still haven't seen anyone really get mad except in cases of direct misgendering. Yes some people will be unreasonable, but they are the exception.