Because something is philosophically "voluntary" does not mean it was done for free, it simply means that it was done in an agreement where force or the threat of force were non-existent.
And to answer your question, if there were no governments and no taxes, then infrastructure would be built as needed, and not prescribed centrally by planners who do not understand the infrastructure needs of various areas. Furthermore, costs would be greatly reduced because of the introduction of competition (private cartels would not monopolizing gov't contracts). Finally, it would be foolish for a company to pour a bunch of money into building and maintaining roads that no one uses—and yet the federal government does that kind of shit with taxpayer money constantly, and doesn't even maintain the existing infrastructure when needed!

All the infrastructure should be auctioned off to the highest bidding companies in a crypto auction, with profits being burned as part of the "orderly dissolution of the federal government" as Adam Kokesh calls it.