I don't have any inherently issue with CoCs, though I find it irritating when threat of "enforcing the CoC" is used as a method to silence legitimate, reasoned criticisms.
The "What We Believe" section certainly has lots of open-ended language; it's quite easy to declare any unwelcome criticism 'unconstructive', or any dissenting views 'tactless'. But the "Don't" section is quite a bit more concrete, and mostly wouldn't apply. Was the implication that "this is a fundamentally bad idea" counts as "derailing" or "unstructured critique"?
https://github.com/ampproject/amphtml/issues/13457
https://github.com/ampproject/amphtml/issues/13597
and the resulting(check the timestamps): https://github.com/ampproject/amphtml/issues/13603
A response like this shows that they really were in a bit of a blinder there for a sec :)
Advertisers will put the advertised price in a hotlinked image served from a server, and they will both (1) use the image being fetched as a proxy for the email being downloaded/opened/read, and (2) change the contents of the served image after-the-fact. ("Save this email and open it every day this week for a new deal" and other horrors.)
Alphabet's Code of Conduct can be found at https://abc.xyz/investor/other/google-code-of-conduct/ . I'm pretty sure "all our users" is intended to include advertisers and rightsholders (like music labels, movie companies).