“It is not “shutting down the debate” if we refuse to discuss, for example, whether trans women are women; to hold such a debate would itself be immoral."
Nope, it's not immoral but it's pointless. On the one hand you'll have the people who understand biological reality gender-critical feminists who'll insist that men cannot become women however much they might want to, and on the other you'll have TRAs and others who have lost touch with reality screaming that there's no debate and anyone who says there is must be a fascist. So there's very little point in discussing it and I don't blame you for not bothering. But let's not pretend it's immoral.
"No serious discussion is ever held in progressive circles about whether human rights should apply to all human beings, for example, because a truly just society should stand upon certain bedrock principles which are not up for debate."
Agreed. As all the GC feminists I've ever read or spoken to have also said. But applying human rights universally is very different from the claim that 'transwomen are women'. You make a mockery of human rights by suggesting equivalence.
How about some serious discussion of women/trans people in sports (there's lots of ambiguities left to discuss like how transmen can be enabled to compete fairly), or as this is Scotland how the census can be framed to protect the privacy and dignity of trans people whilst still providing the robust data that policy makers need, or how gender should be taught in schools, or any other of the really serious discussions that should be happening in progressive circles, but aren't because people like you are saying no debate? Just a thought. But hey, I have absolutely no place in your bookshop or at any of your events for saying such a thing.