[All these points apply to sex and to gender, so for ease of reading, I'll just discuss gender]
Gender-exclusive groups are common in many societies, such as men-only and women-only social clubs and casual activity groups like a men's bowling group or a women's reading circle.
Sometimes this is de-facto, but sometimes this is enforced by rules or expectations, treating the club as a safe space for airing issues people have with other genders, or avoiding perceived problems with other genders.
I came across this old comment in a garbage subreddit by accident when researching. The topic is Men's Sheds:
"Here's the thing. No reasonable person has an issue with women having their own women's activity groups. The annoying part is that whenever men try to do something similar, that's a problem. Women either want them banished or demand entry, EVERY time."
I think their claim is nonsense, grossly exaggerated at best. I also know of many counterexamples of men trying to get into women-only groups (as an extreme case, the Ladies Lounge of the Mona art gallery in Australia was taken to court for sex discrimination, with the creator claiming they would circumvent the ruling by installing a toilet). But nonetheless, I can understand why they feel this way, patriarchal social relations change how most people see men-exclusive spaces vs. women-exclusive spaces.
But my response to their claim is that, I am reasonable and I do have an issue with any group setting up places which discriminate based on gender. These safe places can form as a legitimate rudimentary form of protection, yes, but they maintain and often even promote sexism, and should all be challenged and turned into something better which serves the same purpose.
Of course, I'm limited by my own experiences and perspective, so I'd love to hear your opinions on the topic.
Bonus video: "Why Do Conservative Shows All Look the Same? | Renegade Cut" - a discussion about fake man-caves and sexism.
Not every men's group is a shitty stereotype. It does seem unacceptably common, though. Not every women's group is a safe space, and some are just as toxic and abusive as the far-too-common men's groups. Do we ban them? I don't think we can. Because women's shelters need to exist even if men are domestically abused too and never in my fucking life have I heard anyone suggest a battered men's shelter might even maybe be a good idea. Okay, fine, so violence and safety reasons … Except, shit, not everyone is hetero… A same sex partner can probably find out where women's shelters are. And men are abused to by their partners, men and women, in alarmingly higher rates than anybody seems to take note of. And what do you do with Trans folks? Because their rights are human rights too and why the fuck do we still need to explicitly say that anymore? sigh
And that doesn't even begin to cover social groups.
I guess if you're not an asshole, a bigot, an abuser, or whatever … best you can do when you encounter these things (and you will) is ask yourself whether something gendered is reasonable or not. The answer might be yes, or no, or conflicted either way. I'd like to say that it should be okay if we don't agree about the answers. I'd like to say that people should be able to accept that the other person is making a good faith effort to determine the relative "okayness" in an individual case with an individual perspective. Sadly, we humans seem not to be wired to do that. I'm just gonna continue thinking gendered stuff is pretty dumb on the whole with a couple of conflicted views on a couple of specific things because I know I don't live in a perfect world.
I don't know where you live but men's shelters are a thing. At least I know about them in Germany, the US has them, too. A large problem for men's shelters (and why there aren't as many as women's shelters) is that they want to have only male staff (just like women's shelters employ only women as staff), but there are less men going into social work. Also, men's shelters don't get the publicity women's shelters get, so that is definitely a thing that should change. Men talking about being abused by women should be made more normal and I think it would help if there were more stories in the media about men fleeing from abuse and going to a men's shelter. That would make the concept more widely known.
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'.
The comment you replied to is just "not all men!," but group-flavored. You're right to call it whataboutism.