Most other open source software projects have adopted similar guidelines and they're thriving as well. Taking Rust as an example, they manage to put out high quality releases every six weeks. Thousands of developers of all backgrounds have contributed, which makes me think that the Code of Conduct has encouraged more participation rather than less.
There are dire warnings in this thread about how Wikipedia is going to burn to the ground because of this change. Based on experience of Go and Rust, I'm somewhat skeptical.
I don't actually mind them. They pretty much can all be boiled down to please act as a reasonably well adjusted and decent human being to a point I don't really see what they actually aim to achieve. I fail to see how writing a set of vague rules are supposed to solve deep cultural issues in a community but I guess that at least signal a willingness to tackle the subject which might in itself be enough. Anyway, if it gives some people a warm fuzzy feeling, I'm all for it.
What I find really amusing however is what they say about the culture of the people writing them. For exemple, I have always found it very amusing that the Rust code of conduct feels the need to explicitely address avoiding overtly sexual aliases as its second point, a long time before condemning harassment.