Another possibility is that we are seeing the 'I'm gc, but...' on a.larger scale.
Most people, other than the very deeply batshit, are starting to grasp the issues.
It's obvious that males in women's prisons and sports and rape shelters is insane, and most people would struggle to defend those positions. Toilets and changing rooms, too, the SC judgement has probably brought that into focus.
The very real risks of voyeurs and fetishists seeking access to all those spaces is clear. Safety is an easy requirement. Fairness in sport, ditto. Anyone can see both the risks and the possibility of bad actors abusing the opportunity to 'identify' into those places.
GG and the WI move the focus to slightly more subtle issues, namely social/educational groups.
For girl guides, the argument is "these are children and therefore boys are harmless'. We'll also see a heavy dose of 'poor vulnerable marginalised' here.
For the WI, the argument is that it's just a social, the women aren't vulnerable.
For the GG, there are serious safeguarding issue around camps/sleepovers, but leave that aside for the moment.
Women's and girls' groups, as for single sex spaces, were set up for reasons. Back before the great 3rd wave of feminism, which arguably eroded as many rights as it establshed, it was clear. Girls and women often benefit from the company of other girls and women, without boys or men. Many reasons for this. We think its so obvious it doesnt need explained, but they may all need to be spelled out again.
'Privacy' 'dignity' and 'safety' are easily understood, but single sex associations may need reiterating. These are for equity - to allow.women to talk without inhibition, or interruption, or the verbal equivalent of manspreading. The WI and GG charitable aims will explain them simply, so simply perhaps that we take it for granted.
Women's argument here is quite simple and follows the thinking of the law:
If something is marked 'single sex', as 'for women', then there's a reason for it (LRPG). If you've made a group that expressly excludes men, then it excludes men.
And as the SC found, you can't include 'men in certain clothes' while excluding other men.
The choice is very simple - we either have single sex exemptions, or we don't.
The issues here are men and boys using women and girls for validation or gratification, or 'affirmation', or grooming, and the effects that has on women. It may not on the face of it enable abuse like prisons, loos, etc, but it will undermine and erode women's spaces and groups, inhibit women, and lead many women to self exclude.
This leaves plenty of space for people to argue that sex.segregation is no longer needed and should be scrapped - this would be legal, so if either GG or the WI were to become mixed sex, this would be consistent.
I think it also leaves space for people who've invested in 'be kind' to displace the discomfort and cognitive dissonance they feel at dawning realisation that that argument put rapists in women's prisons, by a very loud defense of how they think we (terfs) are horrible and nasty and they are still kind and pure and good allies, and will openly welcome men into social spaces.