There's a certain sort of man that will never forgive women for "encroaching on male spaces" such as golf clubs, at a time when there was no other way for women to have access to activities and facilities that had been established by and were ruled by men but depended on wives and daughters to service them: "making teas", running raffles, etc.
They like to make a point. They might not have been around at the time but they imbibe the bile from their forebears and they have a skewed understanding of the history. The history that relegated women to the role of "supporting", of "mothering" and did not welcome women as equals.
Their privilege was to have spaces where they could fart and cuss at will, decide affairs of state, have "boy's clubs" of all ranks and stagger home when the mood took them to rule the domestic roost.
Now that women have the freedom and wherewithal to earmark their own spaces, I do not see women insisting that everything that they started must be single-sex and at the same time that everything that was male-only must become mixed-sex.
Most men "get it" and understand that as a society we have moved on from the sort of sex-segregation that reflected the "Upstairs-Downstairs" class-difference between men and women, a hangover from the time when women were legally the property of men. Not all men "get it", unfortunately.
I have lived through times of being yelled at and physically manhandled out of a couple of CIU bars because it did not occur to me that women were banned. The "space for women" in those clubs was usually a behind-stairs, grotty, dirty den like the spaces later designated for smokers. (ie. when smoking was allowed indoors but in a separate space).
The "military choir man" and his brothers are still fighting that rearguard battle against women. I have worked on military bases. If women on military bases say that they need time together away from men, I am going to believe them and I am not going to think it is because they are nasty, mean, selfish people.
If non-serving men need time together, I can understand that. But any man who insists on being included in a women's group, just because there are not enough men with the same issues that he has, is not recognising that his issues are different. They are analogous - but different. This is not the same as women wanting to play golf, FFS!
Personally, speaking for myself only, I am willing to cede "men's spaces" where they can fart and cuss at will and talk, if they wish, about "men's issues", in exchange for women's spaces where we can fart and cuss at will and talk, if we wish, about "women's issues" - and be safe from physical and sexual assault by men and their tedious need to use women as ego-fluffers.
Mixed spaces and groups have their place too, obviously. I belong to some mixed-sex musical groups. The ones led by men are the ones riddled with toxic back-biting, malicious gossip and tiresome horn-locking ego-wrestling - all initiated and kept going by a handful of men who look at any social gathering and seek out not companionship but whatever bit of limelight exists and, if none exists already, whatever they can manufacture for themselves.
To mix metaphors, they will cock things up by creating a dung-heap for themselves to crow from. It is the mixed groups led by women that are the more welcoming and comfortable. However, it is at the cost of women having to spend time and effort managing the disruptive man (or sometimes men) and evicting any who make things so unpleasant that other people start to leave.
It only takes one man to poison things, it can take a long time for a group to recover and it is never quite the same again. It has lost that "safe space" feeling and in mixed-sex groups the other men are as much unsettled as the women.
Men who cannot behave in mixed-sex groups are more than welcome to have their own single-sex groups. Women who want to avoid the extra hassle entailed in belonging to a mixed-sex group should be allowed, without being challenged, quizzed and criticised, to exclude men.
Finally . . . choirs . . . I sing, I know about arranging for voices. Maybe this man does not understand, or want to understand but if, when it is explained to him, he still "does not understand" then he is going to be a liability, in any choir, whatever its make-up. Choirs are, by definition, a team effort and require team-players. PPs have covered all the technical issues to do with singing and choirs so I am not going to repeat them.
HAPPY INTERNATIONAL WOMEN'S DAY