I agree that a CoC by itself doesn't do anything. But if you want to do strict moderation, you need to put in place some rules that you can use to guide moderation and to make it transparent what the rules ares whch govern this moderation.
Otherwise you end up with arbitrarily enforced rules, created ad-hoc by whoever is doing the enforcing, without a way to know what they are or a way to appeal if you feel wrongly moderated.
Good. Otherwise people will pretend to be a laywer and talk about how _technically_ the rules don't say specifically what they did. Its a waste of time.
But really, in all my time on github and gitlab I have never seen an actual contributor violate common sense and common decency. The only shitty things I have seen have been anon users piling in on issue threads which have gone viral and in that case you just limit the repo to contributors only.
Otherwise you end up with arbitrarily enforced rules, created ad-hoc by whoever is doing the enforcing, without a way to know what they are or a way to appeal if you feel wrongly moderated.