Specifics matter. There can be no one discussion norm to get people to be nice to each other.
I think things like discussion norms are highly contextual. The platform in which the discussion is happening, the point being discussed, the people who are involved in the discussion are some of the many factors that could end up mattering. Given these factors, transporting discussion norms from one virtual place to another might not be the right way to think about it.
I think the “EA-like” discussion norm is a function of several things. In addition to the factors mentioned above, the concept of EA itself seems to ask for people to be uncertain and humble.
Consider the following thought experiment—say you took all the same people from the EA Forum and put them all in a Facebook group. Do you think the “EA-like” discussion norms currently here would be maintained? Or imagine putting them all in a forum, not about EA or Philosophy or Sciency stuff. What would happen?