Right, it’s off limits by the Peace Treaty on the public forum.
In private messages you can say what you like. Mods cannot even see those unless you invite them, which can happen in cases of people abusing the PM system to harass or bully people when they need to call in help (you can flag PM posts too).
It’s also possible to convert a topic that’s going that way into a group PM so people involved in a conversation can carry on between themselves.