Personally I'm skeptical about them. People who behave badly will behave badly. People who don't generally won't. The drumbeat of CoCs may make some difference at the margins but I'm skeptical. In any case, as you suggest, a refusal to have a CoC is itself a political statement that sends the message that you don't believe in good behavior and is pretty much a non-starter for that reason.

In general, they're well meant. And in my experience issues arise not so much from the conference organizers but some attendee taking offence over something in a way that most would consider hypersensitive. And the organizers feeling they have to take their side even if they personally disagree.