The honest version of the argument would require its advocates to say plainly: we want the legal category “woman” to be defined by identity rather than sex, and we want that definition to take precedence over the sex-based protections women currently hold in law. Made plainly, that argument would lose. It would lose because most people, without requiring a Supreme Court judgment to guide them, understand that bodies are not merely opinions about bodies, that the reality of male violence against women is not dissolved by a change of identity, and that half the population did not spend a century fighting for legal protections only to be told those protections were a form of prejudice.
This is why the TRAs' response in the last year has been so incoherent, relying on vague legal challenges to FWS itself, political manoeuvres to stall its implementation, and naked appeals to institutions to break the law by ignoring it, when the logical response would be to lobby for an amendment to the law. They know that doing the latter would reveal what they're really about.
I don't agree that EA2010 was not intended to have the GRA applied to it. It was a mistake, for the reasons set out in FWS, but it was not accidental, as the explanatory note to Schedule 3 Paragraph 28 alone proves. Lord Tebbit pointed out all the potential problems when the GRA itself was debated years earlier - and EA2010 paid lip service to that, but its attempts to provide even a minimal bit of safeguarding were obliterated by TRAs. They overreached.