[vertex-four]

As somebody who has experience moderating groups without explicit rules - the result of this in a group of more than a dozen people is inevitably that some of them will feel that (a) the banning is unfair, no matter how egregious the behaviour, and (b) there should be a set of written rules for the leaders/moderators to follow, so that people understand clearly what is expected of them. You really can't win.

Personally, I tend to steer on the side of a broadly defined CoC backed up with a very clear dispute resolution policy (there's plenty of examples of both of these - Debian has a pretty decent set for large projects). In a functioning community, reaching for this should only be required very rarely, so they shouldn't affect anyone most of the time - and they quite obviously don't in the case of open-source projects, or we'd hear about actual cases where people have been kicked out of projects for very little a lot more than we do.