Pete Boettke’s recent post on the deep importance of public choice  prompts this modest thought – one that I am vain enough to fancy supports Pete’s point. My thought is this: for a social scientist to assume away public-choice  problems is not akin to a physicist studying the law of gravity assuming away, say, air friction. It is, rather, more like a physician assuming away human mortality (or, indeed, like a physicist assuming away the law of gravity itself!).
Choosing assumptions for scientific theories is always a matter of judgment. Reasonable people can and do disagree over just what set of assumptions – for whatever is the particular purposes of the analysis at hand – are wise and enlightening and which are unwise and benighting. But to assume away human nature as we know it – or, worse, to assume that human nature as we know it operates only some of the time and not all of the time – strikes me as emphatically unwise and benighting. The assumptions demanded by public-choice and (for lack here of a better term) Austrian analysis  are nothing more than the recognition always that human beings (1) are self-interested; (2) generally respond predictably to incentives; and (3) have very limited cognitive capacities.
Any policy that can be imagined working well if these assumptions are dropped is simply not an appropriate policy to which real-world alternatives can be usefully compared.
Air can, in reality, be eliminated in the space through which a ball falls to earth. Or perhaps more correctly, in reality some actual approach in the real world can be made to eliminating air friction. The features of humanity mentioned above, however, cannot be eliminated. And there’s not the possibility even of approaching ‘in the limit’ their elimination.
There is nothing beyond the banal about reality that we learn when we imagine a world populated by people who, when acting politically, are selfless and in possession of superhuman knowledge. Again, such an imaginary world is not only impossible, it is unapproachable. And so for any social scientist to describe how a policy might work if all or some of these features of humanity are assumed away is very much like a medical scientist assuming, say, that the human body is impervious to bullets shot from a gun or that each human heart is destined to beat for an eternity. Such a “human” (so called) can, of course, be described. And we would all marvel at his or her physical qualities. Indeed, each of us real humans will correctly recognize the banal fact that the closer we approach to being physically like this imaginary indestructo, the longer we’ll live. But nothing that any medical scientist is likely to learn from assuming that humans are indestructible will prove useful in helping that scientist improve the actual practice of medicine.
In short, theories that describe what the world would look like in the absence of the realities emphasized by public-choice and Austrian scholars do not reveal to us ideals to which reality can be constructively compared. Instead, such theories reveal only pure fantasies – intellectual curiosities as useful in making sense of social reality as are the ancient Greeks’ assumptions about the Olympian shenanigans of Zeus and other gods in making sense of physical reality.