My mind has been going like yours, Catiette
Imagine, Men, you lived in a world where there were no women at all but instead there was another entire sex class of people who were almost without exception more powerful, more privileged, stronger, taller, faster, more violent than men.
Let's call them Giants.
For centuries the Giants had dominated the earth. Their systems, their ways, their ideas - all designed to put the needs of the Giants first. Their privileges gave them access to the top jobs, to political power, to education.
Occasionally, an exceptional man might be able to rise to something like the top but it was unusual and fraught with challenges and dangers and many Giants were not really convinced that men were fully human in the way they were...
Among the 6,500 differences between your body type and theirs it was obvious that physically the Giants were so much stronger than men.
They had on average 40% more upper-body strength and 33% more lower body strength, so if you ever physically struggled or tried to fight with them you were almost guaranteed to lose.
As they were between 10-20% faster than you, if you tried to run away they could pretty much catch you every time.
Above all, they were so very much more physically violent. Just 5% of the prison population in the land were men, 95% were the giants, 88% of them in prison for a violent crime.
99% of the sex attacks in your land were carried out by the Giants and, due to their biology, the Giants could impregnate men but men could never impregnate the giants.
In trying to avoid them, men frequently imposed a kind of curfew on themselves. Men wouldn't ever feel totally relaxed going out alone, in a deserted place particularly after dark or where the Giants were drinking after all you had grown up being told that the giants were especially dangerous then.
Since you were young, maybe even only 5 or 6 years old, you had experienced predatory behaviour from Giants (and, over the years none or almost none from your fellow men) so you instinctively trusted men more.
As you walked down the street at night, knowing that a Giant was walking close behind you, your heart would pound, you might clutch your keys in your hand to use as a weapon, knowing that it was probably futile, trying to remember your self defence lessons, looking for escape routes, safe spaces to go to, checking over your shoulder before you entered your front door. 9 times out of 10 it would amount to nothing but the fear was always there.
And sometimes the fear paid off and kept you alive and your safety depended on always recognising Giants.
Having said all this, many of the Giants were charming and delightful and kind and good - it was just not immediately obvious from looking at them which ones were and which weren't...
Despite all of the above, (and somewhat inconveniently!) the vast majority of men were sexually attracted to the Giants and vice versa, with only a small group of men just attracted to other men and sexually repulsed by Giants.
In this land, there were a few safe places just for men away from the Giants, places where you might be more vulnerable or in a state of undress, separate places for your dignity, privacy and, especially, safety. Many of these were hard fought for and protected to some extent in law but mainly relied on a social contract where the Giants would just keep out.
Men could police their own spaces to some extent, so if a Giant came in by accident or design, they could band together and ask him to leave/appeal to authority, enlist the help of a passing Giant etc
These spaces provided a refuge from the very real threat of Giant violence (as well as a welcome break from the Giant gaze, toxic Giant-inity, Giantsplaining, Giant privilege etc) for old or vulnerable men, religious men, traumatised men, men who only fancied other men as well as any man who wanted to not have to engage with Giants for a bit.
And then one fateful day, the Giants came up with a plan that would work for their unhappy fellow Giants...