Doodledog
*It is quite an obvious and valid question. If you are going to say transwomen are not women but men in frocks or dressed as women how will you distinguish which are natal women and which trans?*
If someone thinks they are really a woman how can it be dishonest to dress as one?
Is this a serious question? How can it be dishonest for someone who is not something to dress as one?
If someone impersonates a police officer, it is an offence. Why might that be? Because if people think someone is a police officer they might allow access to areas that would otherwise be kept private? Because police officers have powers of arrest, and the right to handle others during that process that other members of the public do not have. Because of course it is dishonest, as it deceives people, and that deceit can lead to criminal activity.
You might say that not all police impersonators are doing so for nefarious reasons. That may well be the case. Some people might 'get off' on being mistaken for police officers -autopolicephiles, perhaps? All the same, because some of the impersonators might cause problems it is an offence. This is why the police have ID cards, but these can be faked, and there would not always be time to check out an ID number in a fast-moving incident.
Ditto doctors, solicitors and other professions and trades.
Say you are injured or taken ill on a train, and a doctor comes to help you, are you going to ask for proof? What proof could s/he give? If someone set up office as a solicitor and you go in to get advice, do you ask to see their certificates? If you do, how do you know they aren't fake?
The answer, of course, is that we don't know by looking, and for that reason the onus is on the impersonator to know that he or she is breaking the law, and that there will be a penalty if they are caught.
But I thought we were not prescribing how people should dress. If men are entitled to wear dresses because we are abandoning gender norms you can't then allege that a someone wearing a dress is a deceitful man. He may be a trans woman, he may be a man in a dress it doesn't matter does it? because gender norms have been abandoned. And a transwoman is a woman, she thinks so, many others think so.
Why should your prejudices take precedent?