"it knows how to govern itself".
What is this "it" that this sentence reffers to? Society.
The assumption is that society, or to be more precise the people in a society, will govern themselves.
And now you understand why Anarcho Capitalism will never work. There will always be someone who will try to game the system. Or someone who has good intentions but not smart enough to understand the consequences of his actions.
For society to function you must have an objective party to have a monopoly on the use of force.
