Further (and contrary to the empirical evidence, but absolutely necessary for public choice theory) there is the notion (reified to the Nth degree by Caplan in the links I posted) that people are more rational when they are paying than at any other time.
The irony is of course, that in fact "rational" is in this construct simply a synonym for "miserly." In reality "generosity" is sometimes the "rational" action, but economics does not allow for that.
This is most evident in discussions over intellectual property, where the introduction of the question of payment creates largely artificial scarcity.
If I gain 100 pounds by exploiting someone who has nothing and they continue to have nothing, by economics there is only gain. No loss is measured. Sure you can construct "opportunity costs" models for simple situations, but no-one bothers to do this on a large scale. This is part of why various democratic decisions are so mystifying to economists, they are too lazy to attribute any value to the ending of widespread exploitation that seems (to them) to come at the cost of economic growth.
Whether the increases in the legal protection of intellectual property since 1976 have conferred net benefits on the U.S. economy is uncertain.
For another, F. A. Hayek:
A slavish application [to intellectual property] of the concept of property as it has been developed for material things has done a great deal to foster the growth of monopoly and...here drastic reforms may be required if competition is to be made to work. In the field of industrial patents in particular we shall have seriously to examine whether the award of a monopoly privilege is really the most appropriate and effective form of reward for the kind of risk-bearing which investment in scientific research involves.
