As ~always with gender and politics, there’s a pretty big gap between what is and what ought.
What is: The people who make and seek out men-only groups have a stereotype of being shitty, sexist people. The stereotypes around women-only groups are a lot weaker and less negative. These stereotypes are not rules, but do certainly lead to some social stigma.
What ought 1: In a better world gender-specific groups might exist for people to find support and connection around their gendered experiences. There’s some experiences that aren’t commonly shared across genders and it can be a lot easier and safer to share with people who you know also have that experience.
What ought 2: In a still better world there wouldn’t be a significant desire for such groups because we are all sensitive and caring enough that such a group doesn’t make sharing meaningfully easier or safer, because it’s already easy and safe.


Well, yeah?
OP asked the question in general terms, I answered in general terms. With more specific information you can make a more specific judgement. That’s why I said “stereotype, not rule” and separated is vs ought?
I don’t need to list out every possible reason someone might want a gendered group to show that there is a valid reason. Instead just give one. In fact I avoided talking about domestic abuse shelters exactly to avoid this sort of ‘whataboutism’.