Yours is a rather oversimplified version of anarcho-capitalism. It refers to an entirely voluntary society.
So yes, you would voluntarily choose justice systems (likely offered via insurance companies who would provide arbitration and security services), but you’d also voluntarily choose your money (legal tender disallows this) based on markets, there’d be no entity taxing you for “free” shit that governments hand out but rather there would be co-ops and other systems that you could join/opt into so you’d only pay for services you want to consume.
There wouldn’t be these arbitrary bans on things like online poker, communities could forbid it but if the market wants to provide it they will and there’s no man with a gun to take you to prison for violating a nonsense rule.
It’s more like a 180 from the world as it is now where everything is imposed upon you through multiple levels of government top-down, where you have zero choice in the matter, can’t affect those decisions increasingly as power is more distant and have no recourse to opt out.
Rules would be bottom up, localised and community oriented to match their values with an ability to opt out by moving. Higher levels of governance would exist but they’d again be fewer, voluntary and set by the market. Think of things like internet standards, humans need to cooperate so we’d still have rules like that but we’d be free to not follow any we don’t like and alternatives can emerge (no IP, legal fiction stuff blocking).
The argument that it would devolve into what we have today isn’t correct - todays borders are themselves a figment and constantly changing, look into the secessions in Oregon/Idaho for one example.
I would agree there would always be centralisation tendencies for sure, but the consolidation of power coming off that base would be much less likely. We don’t have that base though, we’re starting from the other end so it’s not a fair comparison.
Anarcho-capitalism is really the natural state of mankind, these figments we’ve created to abstract power are unnatural and that’s why they inevitably breakdown over time.