Law, sure, central authority? It does the opposite, it causes a great deal of misery and chaos. It is unchecked power held by few who won’t give it up under any circumstances, it maximizes the chaos of humanity.

I agree central authority has the potential to lead to complete and utter chaos, like we saw in countless wars particularly WW1 and 2.

Both groups would show up to the meeting and either reach consensus or leave it to a democratic vote.

Or they'd decide to cling to their own power. It all depends on which individuals get to any position of power. In an anarchic society, smaller amounts of power can go a lot further. A militia of 10000 men roaming through a decentralized federation of people has the potential to do a lot of damage. With monopolized violence that militia would have a difficult time ever forming.

Most of my thinking is in regard to a state like America turning into an anarchist society. Given there's 350 million~ Americans, it's a certainty that there would be a plethora of groups organizing to solidify their power base. That's why there are no anarchist nation-state sized population to look to as an example for the hypotheticals I've posed. Any opportunity for anarchism has already given way to a centralized government.

I can come up with countless theoretical disasters, and real ones for capitalism.

Wherever humans are involved, there will inevitably be disaster. There are many, many valid critiques of capitalism, especially the digital corporate capitalism that has taken over.

They can choose not to do it, of course. There’s an idea of mutual aid, I scratch your back, you scratch mine, the people would be grateful for them doing a good job and would help them elsewise, as just one example. Mutualism actually has various currency-related anarchist strategies, a central authority is not needed for making a currency valid, I don’t know why you believe that premise to be the case.

What would this look like in practice? If you lived in what is now California and you wanted to sell to someone in current day New York, what currency would you accept in lieu of money within an anarchist society?

Sparta, the Third Reich, the French Revolution, Chattel America, the British Raj.

My point here is that a lack of a central government will naturally lead to some sort of central government establishing itself. It could come from inside or from an external threat. It's possibly that that government turns out to be authoritarian and oppressive, like the ones I mentioned.

For instance, how would an anarchist ethnically Jewish society hold out against an industrial Nazi Germany should they be so unlucky to simply exist next to them?

The British Raj managed to establish itself and rape India for 90 years even despite there already being established governments in the region. Imagine how powerless an anarchic Indian society would've been to defend against the British Empire at it's peak.

Anarchy is not sustainable. That's why we should strive to put in place a good and equitable government to protect us from that possible tyranny. The problem is the same human forces corrupt government's too.