...To impose rationing, Ayn Rand explained in a letter to a friend, means "to distribute [goods and services] in a certain particular manner–by the decision of an absolute authority, with the recipients having no choice about what they receive." Rationing means that the government decides how much of some good or service you are allotted.
This bears no relation to what happens under the price system of a free market. On a free market, goods and services are not rationed. They are produced by individuals and then voluntarily exchanged for the goods and services others have produced. A craftsman builds a chair, which he sells for money, which he uses to purchase a doctor's services. A doctor trades his services for money, which he then exchanges for a lawnmower.
The difference between prices and rationing is the difference between you choosing what groceries to buy and the government telling you what food you're allowed to eat.
Commentators like Singer treat those two as equivalent because, on their view, goods and services do not belong to the individuals who produce them, but to society. They hold, in effect, that brain surgeons and MRI machines are the property of society, which has the right to distribute "its" resources as "it" sees fit. But a doctor's services or a hospital's equipment are not social resources. They are created by individuals, and those individuals have a moral right to dispose of their time, effort, and property as they see fit. Rationing deprives them of this right.
Watkins makes a critically important distinction between rationing and the operations of a free market -- one that even many conservatives who claim to support free markets often fail to make.
When such conservatives wrongly accept the premise that the market is just another form of rationing -- just "rationing by price" rather than by government decree -- they merely set the stage for leftists to claim that government decrees can be a more "fair" method of allocating goods.
By drawing the proper distinction between free markets and rationing, Watkins shows that it is only the free market can create a morally just distribution of goods and services. Only the free market protects the rights of the producers who create those goods in the first place to trade with willing consumers on terms they find mutually acceptable.