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
One major criticism of things like Discord is that they're private, so I don't think that it's inherently disqualifying, some people might even prefer it for that reason. But it's very, very important that you're very clear about this, up front.
Second, the moderators can choose to remove someone who has joined the community in bad faith.
Third, it is entirely different than broadcasting every single action taken by every single user in every single community on the entire protocol to anyone with one URL.
unless you prevent new members from reading the chat history until given permission then they can already read everything before they are kicked out, and they can come back with a different account.
you also can not detect people acting in bad faith if all they do is read.
basically, you can't expect privacy if you don't limit members to people you know and trust. that goes for any group chat, encrypted or not.
i also doubt that discord chatlogs are encrypted on their servers.