You're very much misrepresenting how anarchism is supposed to work with that "automatically" statement. No one thinks if will happen by itself, there's a whole library on thought on how to go about making it the societal norm, with quite a lot of good points that humanity already largely acted like this for most of its two to three hundred thousand years of existence.

Supposedly, anyways. I suppose paleolithic man might well have been selling mammoth futures and executing debtors in the street.

But I also don't really buy it in a urban society unless that society is largely run by the Culture's Minds.