Absolutely not. The default economic system is anarchy, also known as sharing and mutual aid. You see this even in the reddest of US states, where disaster victims help each other, and a huge pastime is sharing food via potlucks. But all evidence points to anarchical/egalitarian cultures as the baseline mechanism of human organization from prehistory.

Externalities don't exist in anarchic systems, because there is no hierarchical separation between producer and consumer. You can't push off costs to some members of the community when they have equal power to retaliate in kind, and there is no incentive to do so.

> Externalities don't exist in anarchic systems

Sure they do. I do a thing, it benefits me but causes a problem for my neighbor in the process, I say "oh well fuck him", that's a textbook externality.

> they have equal power to retaliate in kind

A convenient fiction often engaged in by proponents of anarchy. In practice if you compare pairs of people at random you will find almost none that can reasonably be described as equal. Equality is something imposed by the law in an attempt to improve our lives on average.

Anarchy lasts exactly as long as it takes people to start banding together and no longer.

Ok so you’d win a community upstream on a river and you build a dam and hive off the water

Downstream 500 miles away another community loses their water source

Those externalities still exist

Haiti is in Anarchy. All sharing and mutual aid is shadowed by resource and power struggle. It is even worse than communism and fascism.

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Externalities don't exist in anarchic systems

Neither do computers.