I think "play nice" is a good rule, but can have different meanings to people. For me, just if I was running a forum, I would want to avoid personal insults. In other words, a serious even intense discussion is a good thing, but if you disagree with someone's premise or facts or mantra let it be about the facts. There is a topic on this EAA forum just a few days back where someone calls another "an idiot" because he is not aware of something about aviation. The one calling the names doesn't even know the other person, no way of knowing if he is smart or not. "Play nice" can also be a cover really for don't post anything that doesn't agree with what's already on the forum, no rocking the boat. Lots of people like that.
We have a local conference Idea Fest, run by Walter Isacson, formerly of Time Inc, where they invite prominent people from all over the world and all walks of life, lots of businessmen, world leaders, sports figures, authors, and on and on. It covers all spectrum, one side to the other, the good , bad and some of the ugly. It is very well attended and exciting to hear. Each person accepts be nice in that they let the other speak , no interuptiions and it is a discussion to enlighten and maybe solve problems rather than just a debate to win a point or have your client win in court. I think it is great. It aint too hard to get folks to come to the mountains and stay at a lovely resort on the banks of the river!!
Incidentally, Walter has a book about DaVinci where he picked him as the smartest person ever because he was so curious and wanted to know about everything.