Mayor: Periodically an ice cream company will hold a free ice cream day as a promotion. Showing up may not cost you any money, but it sure does cost you time. We learn from this that when something valuable costs no money you get overconsumption and long lines. Currently, those who drive to work complain about the congestion they face in their rush-hour commutes. What is needed is a system for charging people for the use of roads during rush hour. Then rush hour congestion will abate.
The claim that when something valuable costs no money you get overconsumption and long lines is a general claim used in support of the argument's overall conclusion in the mayor's argument.