Utopia like Anarchy severely ignore the "human nature" factor.
In no way are modern nation states a form of "free association". I cannot freely choose to not pay taxes if I am born in a nation, nor can I freely choose to join another nation if I accept their principles.
Your predictable and very unoriginal use of the "human nature" argument is in fact the ignorant position. It completely ignores the significantly larger number of humans throughout history (and including today) that have lived in freely associating relationships that in no way resemble the modern nation state or earlier forms of civilisation.
You cannot find a single example of what you deem "free association" that is not currently defended directly or indirectly by an army.
The irony of your statement is that while you called me ignorant you said the exact same thing as I said in your first paragraph.
Then you try to back pedal to make a "point" in the last one by giving zero examples of your "larger number of humans throughout history (and including today) that have lived in freely associating relationships.
And next time refrain from calling other people who disagree with whatever ideology you believe in as "ignorant", it qualifies you as a troll.
So like what's been happening for the last 2000 years and resulted in our current borders?
For examples of how order is maintained, just see the Tiananmen Square protests