" I continue to deny that there is any legal violation of any kind going on here, which is a straightforwardly true position. (The UNDoHR has no legal force in the US, of course)."
There is no legal issue here when it comes to how you refer to people. That is true.
There is likely a legal issue when it comes to how her parents destroyed her; but that is down to what the legal definition of abuse is...
So i'm not argueing that it is illegal; no, but i am argueing a moral standard.
"I might consider it degrading to have somebody disagree with my religion (which is certainly part of my identity)" - actually yes; I could tell you that you worship god wrong, and that you're going to hell. You might shrug that off, but if everyone everyday told you this - or implied it by their choice of pronouns - you would find it very damaging.
If your parents told you that you were going to hell because of this part of your identity, you may very well try to change it. But unlike religion (and this is where your comparison differs) it is very hard to change your gender, i would like to claim it is impossible, but i'm not everyone, but most people aren't able to change their gender.
I believe it is a biological fact, set during development (much like sexuality) It is the way God made you; if that helps.
I do know people who have changed their religion - and not to dismiss this point, it was a part of their identity, and their identity changed - but then we're always changing. Some things are not as flexible. (though people who identify as genderfluid would i suspect claim gender is flexible, i'm only sure that the trans-gender and cis-gender people i know do not believe their gender is flexible)
"degrading here is carrying its traditional connotation of behavior that would be universally recognized as extremely humiliating."
Fair point; and i'm glad you agree; thus i will state for the record, i believe it is universally regarded as extremely humiliating to misgender someone. If you, for example, were called a women, you would be humiliated. Is that a fair comment?
"If you want to label, and prosecute, this as abuse, then you need to say any comment calling someone fat or ugly, or disagreeing with religion or politics is hate speech and abuse as well. You are cherry picking this." - Im using this big media sensation as an example in an attempt to educate others.
Are you saying that so long as any injustice is left in the world that we shouldn't address any of them? Cause that's great.