"Who will build the roads?"
This is the typical question that anarchists / libertarians get when they talk about living without a govern-cement.
People are so conditioned that only the govern-cement can handle such large amounts of money and get anything large accomplished. Of course, that is mostly because they block anybody else from competing with them. (unless you pay lots in campaign contributions).
But, who will build the roads?
And the real answer is, "I will."
I have built roads for many people.
Mostly they were developers who paid for and built the roads.
(And then they gave the roads to the state, so they didn't have to maintain them)
You might more accurately ask, why do you insist on paying 4 to 10 times the amount for crappy, pot hole (un)filled roads? Why do you insist on paying so much for so little?
However, none of these mental gymnastics are even relevant.
In the future, the entire argument / counter-argument will seem stupid, insane, inane, off topic.
Because, in the not to distant future the larger problem will be how do we remove the toxicity that is what we now call roads? In the future, roads will be turned into basketball courts and walking paths. People will discuss the better ways to turn these areas into gardens... but that will be short lived as the ground is toxic through and through.
In the near future we will have hovering cars.
Not far after that, we will have teleportation.
Along with this, we will also have tiny, green, electric power plants that can power a small community. Thus, we will see tiny communities springing up all over. As people realize that with modern conveniences like power and water, you can grow all the food you need with only 10 hours a week of work. The cities, and all of their industry will be for the most part, down sized. Made micro. And the mass exodus of cities will commence.
All of this huge areas we call parking lots, strip malls and ROADS, will pretty much be abandoned.
So, who will build the roads? No one.