I'm not sure why there's ever been a need for a code of conduct beyond the golden rule. Just, like, be nice and stuff.
One thing codes of conduct do is clarify what other people are expecting (hopefully they clarify the shared expectations of the group).
The CoC won't help those people in the first place.
I don't think it is a cure all or anything, but it at least provides an opportunity to avoid counter productive arguments, and at worst is still incrementally less arbitrary than banning/shunning difficult people outside of a CoC.
(with apologies to Billy Shakespeare)