Earlier quoted context omitted.
That was always implicit in group discussions. As others have said, Codes of Conduct aren't creating new rules, they're just making them explicit instead of implicit. Let me give you an example: you have a group of friends. Two of your friends have recently experienced a miscarriage. The implicit rules in your group have now expanded to include "no dead baby jokes" (depending on how dark your group's humour was, this…
I agree that if there are rules, it's much better to make them explicit instead of implicit. I also think your example makes sense, but I'm not sure it applies to larger groups or public forums. There are simply too many people to avoid discussing every topic that could offend someone. I'm not saying overt racism or homophobia is okay, but especially when it comes to humor it's almost unavoidable that it can hit too…
The core reasoning behind Codes of Conduct is sound.