Every community writes rules. Most of them are long, nobody reads them, and they exist so somebody can point at a clause after the damage is done. Ours are three lines because three lines get remembered.
Argue with the take, not the person
Disagreement is the point of the place — if everyone agreed there would be nothing to read. But there is a difference between taking apart an argument and taking apart the person making it, and everyone over the age of about nine knows exactly where it is.
A rumour is not news
Post what you like, but label it. The window is the season for confident nonsense, and an account with a lot of followers is still an account with a lot of followers. Anything presented as fact with nothing behind it comes down.
Rooms have to earn their place
This is the one people find harsh. A room that has curdled into four people shouting at each other gets closed, and I do not apologise for it. A bad room does not stay contained — it sours the people in it, and they carry it into the good ones.
Moderation is done by people who are in the rooms, not by anyone watching from outside. If something needs attention, report it where it happened. That reaches someone who already has the context, which is most of the work.