If a man wants to rape a woman in a toilet he will do so - he does not need to pretend to be trans.
A crime requires motive, means and opportunity.
Safeguarding tends to be about about reducing the opportunity, particularly if there are means.
A private space like a toilet is a means. So it's necessary to reduce the opportunity.
If a man is able to loiter in a toilet waiting for an opportunity to isolate a woman, he can commit a crime far more easily than if he will get thrown out the moment anyone sees him in there, or entering there.
The argumentative trick Tandora is employing here is the same as for the 'existence' above. Tandora quantifies NOTHING.
Reducing opportunities or risks, crimes or accidents one-hundred-fold counts for nothing if any still occur.
You reduce road deaths by a huge amount by mandating seat-belts? So what, some people still die.
So if nothing is quantified, there is no measure of success or failure, therefore nothing Tandora suggests can be worse than an alternative in practical terms and outcomes. The only argument is about feelings, or appeals to abstract ideals.