Fair point! A different user has already pointed out that this isn't disclosed enough on the landing page, and I'll be adding a section to clarify that, both on there and in the app itself.

I think one of the replies here already linked the current proposal for private data spaces, which I'm hoping will become implemented later this year. At that point, people will have the option of either having their community be 100% public, or confined to a more Discord-style data storage, where people can still join, but not everyone can "just read" the messages