My main objection to most CoC is this: https://github.com/EthicalSource/contributor_covenant/issues/711. The second problem is that if you accept contradictory notion such as gender identity (that is not capable of giving a clean definition of the terms it uses), you can derive any accusation if you want. If a project doesn't ensure any "checks and balances", it becomes easier to exclude undesired people for alterior reasons from participating. But this is all theoretical, it would require a emperical analysis of actual incidents in the past to decide if CoC are effective, ineffective or destructive.