Code, conflict, and conduct

Here's one data point. As community manager I introduced a code of conduct to the openSUSE conference and was involved in shaping the wider community guidelines. They never had any adverse affect that I could see despite indeed quite some pushback at the time.

The guidelines were used once to push someone out, which had an amazingly positive effect: that person was clearly keeping many others from contributing with their bad behaviour. In hindsight I should have acted far sooner and in the future, when encountering a toxic person, I certainly will. Heck, I have, though mostly I could fix issues by a stern talking-to rather than kicking. But having a CoC to point to and as stick behind the door is very useful. I know several people who don't attend events without one and while as boring white dude I never bothered to look myself if an event had one I fully support that.

Talk to community managers. I bet you won't find one who thinks a CoC does anything other than grow the community.