It's the enforcement. See posts upthread about real life cases of people being pursued into court for not using correct pronouns. Typically autistic behaviour is not accepted as a defense, excuse, reason when transwomen are the aggrieved party!
Think about what it means in a larger sense. Girls can no longer say but he is a boy... when a boy is in what is supposed to be her safe, single sex space. She cannot say that out loud as he is she, and those pronouns MUST be honoured.
So girls are no longer able to say no, are being taught that what they feel is secondary to what a boy might feel.
And what about the boys? Not a stereotypically roughy thought boy? My! You must be a girl then! How screwed up is that?
And feel free to reverse the sexes on all parts of that. It's equally screwed up whichever way it happens. Though oddly almost all of the memes, cartoons and attention seems to be on the males who want to transition.
Pronouns are the tip of the iceberg. They muddy the waters making it hard to say what you want to say without being offensive and automatically in the wrong.
Words are important. They create our social reality. Fuck around with them and you unstitch the mores that make society work!