"At what point do you deem social behavior unacceptable? It's a fine line to draw and one that might be difficult for many communities to do correctly."

This is key. A large part of contemporary American (and, as I understand it, European) politics involves struggles over the size of the Overton window. This means that even people with little interest in the project will have a strong incentive to use the project's code of conduct as a tool for defining the boundaries of acceptable discourse in the communities that overlap with the project.