Even in the comments on this post I can see the argument that basically boils down to “spaces that don’t cater to me should also bear the effort of keeping out of my way” being voiced.

I think that sums it up well, even if the sidebar was presented the very first time someone went into a community, some people wouldn’t read it, some people wouldn’t care about the rules, etc.

So thats where moderation has to step in like happened here. Every community has rules, its not on the community (or the server) to make sure that visitors are aware of them, its on the people joining in on the conversation. I don’t know that there is a better way to present the rules than simply making them available.