Sex by deception is one of those areas that's so interesting it often comes up in law exams.
When I was studying, there was a problem question which put the following scenario: You have two women who are identical twins. One twin fancies her sister's husband. She pretends to be her sister to get the husband into bed. On getting him into bed, it turns out that he has a taste for rather rougher sex, including anal, than she had bargained for.
In this scenario, who's liable?
The man might be liable if the woman clearly says no to being penetrated anally and he ignores that, but he might also have a defence if he reasonably believes this is his wife and they have an agreed safeword.
The woman is definitely liable because her premeditated deception goes against him consenting to sex. Even if he's enjoying it, he's been suckered into it under false pretences.
(Disclaimer: my legal ken may be slightly out of date, but I think I've got the gist)
The clear issue here is informed consent. That applies to a man (maybe young, naive, drunk) who doesn't realise his partner is male. It applies to a woman who pretends to be a man so she can get other women into bed.
I think one of the things that first set off major alarms for me on the trans issue was the campaign to amend the law on sex by deception - am I remembering right, or didn't Stonewall explicitly argue for that at one point? It was a clear signal that a certain caste of people feel that the need for consent doesn't apply to them.