So what? Should they not exist? Why must marginalized communities leave themselves defenseless and accept that they can only have a conversation among themselves in the midst of a hurricane of abuse?

Because they can get so dominant as to alienate normal users. Like in Reddit.

But I agree with your larger point and I think it is a valid point.

Personally I think media like Bluesky are not suited to form these forms of closed communities. There's nothing wrong with closed/gated community and I think it's especially important for marginalized communities as you mention, but I think in 2025 you could do that with a Discord "server", Discourse forum, or a non-federated Lemmy instance.

The problem with folks like this on Bluesky and X is that they want to both have a closed community but also benefit from the easy comings and goings that a more open forum offers. IMO it's a fools errand. There's a reason why the humble group chat has won as the social media of choice for, well, everyone.