RE: the in-between. Under the old state of things, there was trust on the part of women that people knew where they ought to be. And if a woman was butch or androgynous, we trusted that they were female. Sometimes we were wrong, but it was rare.
RE: getting people involved after the fact. This is rather like arguing that nobody should lock their doors out of concern for being robbed, and they should only get the cops involved after they've been cleaned out. You're removing the ability to prevent harm, and placing people - female people overwhelmingly - in a position where they cannot protect themselves from being hurt and can only get the police involved AFTER they've been harassed or assaulted or raped.
This essentially creates a situation where females are being asked to take on real risk and face real harm... in order to avoid hurting the feelings of a small number of males who identify as women and need to be in female spaces to affirm their internal subjective impression of themselves.
I think this is rather like abolishing the sex offender registry, and letting likely-to-re-offend pedophiles move in right next to a preschool, and telling all of the families in the area that it's no big deal, they can get the cops involved after their child has been molested. That's not intended to draw a parallel between transgender people and pedophiles, just to illustrate the insanity of placing that much risk on people in order to protect the feelings of a few.