Unfriendly behavior is not a cause in itself, but a symptom of a deeper problem. Stackoverflow sends thousands of newbie questions to everyone, flooding the reading stream of willing experts with what is spam to them.
Stackoverflow provides insufficient ways for askers (or others) to mark their questions as newbie question, and insufficient filters for experts to allow them to choose what they want to see. What works for thousands of participants does not work for millions.
As an example I prefer to just look at questions who are 5 hours old, have no answer and have a positive score. I might miss a few interesting ones, but avoid most annoying ones. But to do so I have to use a clumsy browser bookmark and a userscript to hide all my search options. Why can't Stackoverflow provide such options conveniently?
This is a sample search query that I bookmarked:
intags:mine answers:0..1 score:2 is:question closed:no duplicate:no hasaccepted:no created:3m..1d lastactive:9d..0d
Facebook has a button labelled "Show me posts like this less often". Not sure how that works, but why can't stackoverflow use this mentality to help readers avoid seeing posts that they do not wish to see?
A different CoC does not change this, just like the last 10 years what was missing was not a better CoC. The CoC is just a meek attempt to appease the PC activists, it wont change a thing.The next logical step is to remove downvoting, because of all the hurt feelings of askers who get downvoted a lot. Downvoting is also "a subtle put-down".
Give experts an easy way to see only expert questions, and experts will stop leashing out against what is spam to them.
This would also help keeping experts interested in the platform, rather than turning away in disgust of all the spam.