Twenty, thirty years ago, there was a tiny population of MTF transsexuals, primarily homosexual, and more likely to pass than now, with a massive lack of public acceptance - similar to homosexuals generally.
Overall, little harm was (immediately) done by unofficially letting them into women's toilets, as to not do so could casually out them in public life, and potentially open them up to significant harm. There was never any serious suggestion of letting them go further than that - into single-sex shelters, sports, etc. And it was always unofficial - if any had given trouble, there would never have been any issue getting them ejected. The potential resulting brouhaha basically guaranteed good behaviour.
Circumstances have changed. Public acceptance of MTF transsexuals and others under the umbrella (transvestites, Alex Drummonds, Pip Bunces) is significantly up, to say the least. And institutional acceptance is beyond a joke (see Harry Miller/FairCop). Many are explicitly out, and those who aren't are less likely to pass any more, given the public attention. The "outing" argument is largely dissolved, due to this combination of acceptance and visibility.
And at the same time there is a massive "thin end of the wedge" push to let any male into any female space for any circumstance, no matter how blatantly unfair or dangerous. Unsurprisingly, there is pushback from women. Including regretting the leniency that was given some decades ago that in some way led to the current situation. It is no longer clear that a woman could get a misbehaving male ejected.
As of 2020 any MTF transsexual who sees the new TRA/MRA activism, and women's rejection of it, and does not realise they should be denouncing it, saying "not in my name", and withdrawing from any attempt to use female spaces, including basic toilets, should be ashamed of themselves.
Any male person continuing to attempt to enter female space in the current situation is clearly far more likely to be someone not to be trusted than a MTF transsexual doing so in the previous century.
Not realising the harm their boundary violation was doing is one thing. Not caring is quite another.