So, there are a couple of issues with this argument, the biggest is this: for the most part, women are not the reason why male "nerds" are social outcasts; that problem is by-and-large other men, and by gate-keeping women from nerdy culture they are reinforcing the very gendered stereotypes and heteropatriarchy that made them social outcasts in the first place. That's self-defeating behavior at best; at worst you're verging into incel "supreme gentlemen" territory. In no actual instances are men seriously oppressed by women, at least not in any broader cultural or structural sense. There is nothing to justify discrimination or gatekeeping against women within this or any other nerd-dominated hobby other than misogyny, either deliberate or internalized.
You must have attended different highschools than everyone else. Sure, low social status people are picked on by men and women, but low social status males are very much treated very poorly by higher social status women. This is true in all societies -- it's not an incel argument (incels go on to blame women and fixate on this blame). It's laughable to exclude women from the social banishment of low status men, just like it's laughable to exclude men (or women) from the banishment of low social status women. However you want to slice it, our society does more to socially isolate low status men than it does to low status women (you can blame the "patriarchy" for this, there's a credible argument that it's the treating of women as chattel that provides value to low status women that low status men do not have).
We, as people, are nasty to each other without engaging in -isms. It should not be an outlandish argument to point out that, especially for young men, the achievement of sufficient social capital to land a mate is of prime importance. With that understood, the prospects of low status men to achieve such is small, so it's attractive to engage in hobby activities where you can pretend to have a much higher social status. It's also understandable that while pursuing this fantasy, actually doing so with women threatens the fantasy, as real social infighting takes place for status in the group (even if the woman isn't available or interested -- we're not that far from apes) and the fantasy status is threatened. So, groups of low status boys wishing to pretend they're big shots socially are hampered from doing so in the presence of the actual object of their real life social goals. You may find this disgusting, but that's ignoring the primary focal point of society -- to provide for the next generation. Almost all of our social rituals are status seeking behaviors to improve our prospects for a mate. Some people lose, and might not want to be reminded of this.
Also, this exact reason is why it's a good idea to have women only safe spaces -- women also wish to escape from this mixed-sex social grind for status. They don't want to put up with socially awkward boys making badly timed and badly executed advances because they think that if a woman is in this group, her social status is low enough they may have a chance. That's entirely mistaken on the boys part, and some serious education needs to go into correcting this, yes, but it's the very reason for no boys allowed, yes? You can't acknowledge the problem on one side and then say it's horrible on the other. And, this is ignoring the real predators and bad actors -- this is just the socially awkward fumblers. Add the other in and yes, women should be able to have safe space play areas. But, so should men.
There are good reasons on both sides to not want to game with the other sex as part of a recreational and voluntary hobby. It turns out the reasons often overlap.
Creating spaces without men, however, at least in context of small online gaming groups, is an actual matter of personal privacy and safety. Sometimes those practical concerns butt heads with loftier ideals. If the levels of harassment against women on the internet, up-to and including doxxing, swatting, and death threats, were not so outrageously out of of proportion I might even be inclined to agree with you. As it is though, the dangers that women face on the internet represent such a stronger justification than "I'm worried about all the Stacys making fun of me" does that "No Women" spaces reek of discrimination while "No Men" spaces seem a perfectly reasonable precaution. Not as a matter of structure, anyway, but certainly as an accommodation on request.
See, you get it on one side, but fail to see how it's also for personal privacy and safety on the men's side. I wouldn't want to play in a men-only game, I don't have that kind of damage to need that safe space. I'd rather people of that desire be able to self-advertise, so I can make informed decisions.
This, by the way, demonstrates the difference between equality and equity. Equality seeks equality of service; equity seeks equality of outcomes. In instances where the playing field isn't level (which is most instances, but definitely includes having a defined gender identity on the internet), equity seeks approaches to make the field more level; in this instance, by allowing for spaces in which women gamers can be reasonably sure they do not have to worry for their safety while play tabletop games.
Who picks what's equal, though? This is the problem with equity as a goal, someone more equal that the others defines what's equal for everyone.
