It shouldn't be that hard to to follow the "Don't be an asshole" rule, unfortunately for the rest of us, 0.001% can't figure out how to get along with other humans.
I think CoCs just become a new tool for a different subset of assholes to abuse. Yes it does suck for those who have a legitimate issue. I've yet to see how CoCs solve that problem in practice.
As I see it, a CoC gives good leadership a way to punish people who are assholes without causing too much of a backlash. Without it people would argue about fair process, not knowing it was wrong, cultural differences, etc, etc. It's hard to enforce a don't be an asshole rule when you mostly have soft power at your disposal. Of course, it also gives bad leadership a tool with which to punish people without causing too much backlash.
I think CoCs just become a new tool for a different subset of assholes to abuse. Yes it does suck for those who have a legitimate issue. I've yet to see how CoCs solve that problem in practice.