>On the other hand, I think gating functions are necessary to build community.

Of course, obviously, 100% agree. But then why is there so much debate in this topic that "men's only social/recreational spaces" are somehow discriminatory? We humans segregate ourselves based on a lot of shared things all the time since childhood.

>Bouldering favors slim people.

You're missing my point. The point I was making is that where I live, what I noticed, is that people who go to perform solitary sports like bouldering, tend to do said activity for the workout itself, not to meet new people or socialize with strangers.

They go there alone or with their group, they boulder alone or together, then they go home, not reciprocate much to chit-chat of others since that's not what they came for. You can pick any other such sport, likes fitness studios/gym, the result will be the same, people go there to lift weights, then go home, any addition chit-chat is more of an annoying interruption from their workout. Sure, people here are polite and they'll answer your questions on technique or to spot you, but they won't open up to strangers and start to befriend you just because you engaged them in some conversation. Social etiquette differs heavily between cultures. Some are more isolationist towards strangers and value personal space, some are more open.

You have better chances in meeting people in socializing at teams sports like football, volleyball, martial arts, etc because the sport itself demands it. Or just to events where socializing is the main activity like concerts, pub quizzes, etc. but solitary sports like bouldering are pretty bad for that unless the bouldering gym is full of posers who only go there seeking to socialize instead of work out (there are some of those in every gym, you see them spend most of the time scrolling on their phone or taking selfies for Instagram stories instead of working out).