You are using national defense as an excuse . . . unless you are willing to demonstrate how the private operation of a road negatively impacts our national security.
I just finished reading the new P.J. O'Rourke book, On The Wealth Of Nations. Talking about pork barrel politics, on page 137, "Public services are never better performed than when their reward comes only in consequence of their being performed, and is proportioned to the diligence employed in performing them".
That Adam Smith knew what he was talking about!