CoCs have a bad reputation because many of them are written without a clear set of rules, often intentionally so that the authors have leeway to adapt the vague rules for new behaviors they want to ban. This can be considered a good thing (don't need to amend the CoC for what is "obviously" bad behavior that the original didn't account for) or a bad thing ("it's not obviously bad behavior, you just made it up so you can ban me via the CoC because you disagree with me").