Thank you! But it seems if that kind of thing consistently worked, the government wouldn't need implicit violent threats either. I like the point about free association, which I can see looks different with governments, and makes me think.
I guess my main question is why think there wouldn't be more, and more arbitrary, coercion in anarchy. For all that's wrong with the US (in my view), even if I had the easy choice to opt out of government completely and go to an old-Australia lawless place, I really don't think I'd want to - and I think I wouldn't want to in large part because I suspect I'd be the victim of way more "might makes right" coercion.
Anarchy doesn't mean "no rules". It means "no rulers". The key to anarchy (and any successful commons) is development of widely-accepted rules (or customs) and a system that rewards compliance and cooperation while penalizing rule-breaking.
The trick is to make breaking the rules more difficult/costly/troublesome than complying with the rules. There are dozens of well-documented ways to do this, but blockchains are a hugely important innovation that will facilitate this in ways that were previously impossible.
Bitcoin provides a perfect example. Anyone can, in theory, launch a 51% attack against the Bitcoin network by acquiring sufficient computing power. However, because acquiring this power is very expensive, deploying it in ways that destroy the value of the bitcoins one would gain from the attack is irrational. Anyone with that much computing power would be far better off economically if they devoted it to mining bitcoins legitimately, and thereby making the network even more secure, rather than to attacking the network and destroying the value of the coins they would gain.
So, in systems like that, there's simply no need for physical coercion, arbitrary or not.
There will always be a small minority of irrational people who refuse to comply for one reason or another. The key is to make sure that their non-compliance doesn't jeopardize faith in the whole system. It usually won't, unless they resort to physical force, in which case the majority who follow the system are justified in using physical force to defend themselves.