Using responsibility might imply a legal burden and unless the maintainers understand they are taking that on, it might be better to ask them to read it before agreeing to it.
Also, it makes sense to at least link to it when asking people if they want to include a code of conduct. Otherwise, I agree with the idea of having codes of conduct and having them be common and de-facto but, it's useless if people don't understand exactly what they are agreeing to.
FYI, I feel this way about including a Free License in your code as well. It's a nice thing to have to blanket cover your code but, the person including it should understand what they are putting their code into and also, the expectations of others who will contribute to the code.
tl;dr, there's a bug where a CoC is created even if you opt-out.
I understand the sentiment, but boy is that a politically charged statement. It amounts to "I don't agree with you, and this is my project, so STFU or GTFO."
The reason is simple: it doesn't stop the debate - it just takes control over the debate out of your hands and puts it into the hands of a disgruntled user who will discuss this in a forum you don't control.
Users who feel they have a legitimate grievance and are cut out of the official conversation tend stop being users, and in the worst case may become the exact opposite of an evangelist for your project - they become someone who will dissuade other users from working with your project.
The marketplace can determine if this is something that it finds to be onerous.