True story:
In the early 1970's MIT had recently "gone co-ed" in the dorms, and historically there was only one bathroom on each floor (for guys) and other than toilet booths, it was open -- a line of urinals and farther back, an open shower room. Basically a locker room without lockers.
So at first to accommodate the girls, they designated the bathrooms on alternate floors for the girls, meaning longer distance to walk and climbing lots of steps.
That didn't last long. A few of the girls started using the boys bathrooms on their floor for convenience. The guys didn't mind, of course. Shortly thereafter a dorm meeting was called, and it was agreed that all bathrooms on all floors were declared "co-ed". There were a few questions, but no dissenters.
It worked great. Later, the first time I visited a friend who was studying there, I was greeted in the shower room by a lovely and quite naked young lady. What to do? I took a shower alongside. It was, as they say, liberating.
OTOH, that sort of informality and easy acceptance wouldn't work these days, and not outside of that college environment. But it was an interesting experience.
As for men pretending to be women going into a women-only bathroom, ummm, no, that's entirely different.
I can see how that could sound like a good idea to a young man in the 70s.
East Campus had some coed floors with 5 bathrooms. They were originally all coed bathrooms. Then at least one bathroom was designated female only. There was also a larger bathroom with two showers in a common area.
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I used to go to a Holiday Spa that was so small (how small was it?) that it only had one locker room. They would alternate men and women each day and night, so Monday would be men in the day and women at night, then Tuesday would be women in the day and men at night. Many of the older guys would swim in the nude.
IIRC, it was Friday that they allowed everyone in. The women had two rows of lockers, the men had two rows of lockers.
And everyone used the same showers, which had shower curtains.