Explicit is better than implicit. Different communities/subcultures have different standards of desirable and undesirable behavior - some communities believe that heated and emotionally intense debate is the right way to get a good result and "decent human beings" have a thick skin and try not to get offended, some believe that this precludes good results and "decent human beings" are empathetic and try not to offend.

Since contributing or maintaining an open-source project is a pretty intense commitment to interpersonal interactions (if we all knew what code was right, we wouldn't need maintainers), it's good to know what beliefs a community has about desirable and undesirable means of interpersonal interaction before you commit to joining it.

Note that as a corollary, I think it's important that there exist communities have codes of conduct that aren't based on the Contributor Covenant etc. Linux's Code of Conflict is a pretty good example: https://www.kernel.org/doc/html/v4.12/process/code-of-confli... If that doesn't sound like it describes a community you'd enjoy, maybe it's good to know that well before you burn out on contributing to Linux (as many technically-prolific contributors have done). If it does, great, you'll enjoy the project and the mailing list.