> There are, after all, certain functional requirements for people to live together in cities and two of these appear to be some sense of private property and protection against violent crime. Another is management of infrastructure.
Another is food, which most people agree is more efficiently produced by a competitive market than by central planning.
> The government, however defined, must monopolize them because otherwise you give tremendous power to the hands of private corporations. At least with a government there are political constraints that there are not with a corporation.
And yet, what I'm saying is precisely that private enterprises would lead to a better society not just for me, but for the vast majority of people as judged by their own personal subjective preferences. That includes most people who oppose by suggestions.
> I haven't yet met a libertarian who thought that murder should be legal absent a contract to the contrary
I haven't yet met a person who thought that. So why exactly do we need government to "make murder illegal"?
> nor have I yet met one that thought that big business should be able to control all roads and exclude whoever they want from travelling.
Depends what you mean by this. I personally believe that if you own a road, you should be able to exclude others from using it. A polycentric legal system, like any other system, would lead to a convention or set of conventions for what constitutes "property rights" that is economically efficient.
> So the argument is over a decentralized government model vs a heavily centralized government model.
This obviously comes down to your definition of "government." In the broadest dictionary sense of the word, yes, it could refer simply to any mechanism that arranges the affairs of a group of people. When I use it, I intend to imply that I am talking about states, namely nation states and the subdivisions thereof. Lots of anti-state libertarians have offered detailed definitions of what constitutes government in this context. Murray Rothbard defined the state as an organization that claims monopoly legal authority over a region and funds itself at least partially through (compulsory) taxation. I prefer David Friedman's more enlightening definition. He defines a state or government as an organization which most individuals in a region exempt from their normal perception of personal "rights." If a random person attempts to forcefully take money from you, chances are you will fight to resist, or at least consider it a wrongdoing, and most of the rest of society would be on your side (assuming the evidence is conclusive). But when government forcefully takes money from you, you probably won't be very upset, and probably won't resist even if you are upset. And the majority of society will not consider this a misjustice.
> After all, does it really matter whether a city is formally private or public sector?
I think it does, because the "private sector" (assuming you mean a competitive market) will be more economically efficient.