This is admittedly a simplifying assumption, but it is the basis for the enormous analytical leverage economic theory in general, and public choice theory in particular, is able to apply to our understanding of social interaction. It should be pointed out, however, that the assumption of self-interest is not as restrictive as it is commonly made out to be. It is undeniable that people value a wide range of things not normally thought of as economic goods and services. Among the non-economic items that people value are their opinions and beliefs. Certainly nothing in public choice theory rules out the recognition that self-interested people may want to promote their vision of the good society.
Caution has to be exercised here, however.
If we attempt to explain why people act on the basis of ideological considerations by simply putting an ideological variable in their utility function have we not, as Machan says, made 11 shambles of the explanatory value of the economic man model. Any . . . While this point is well taken, and does indeed indicate a risk, this risk is avoided by making sure that we go beyond simply explaining that people behave ideologically because they want to. The public choice model does go beyond this obvious tautology by predicting that people will behave more in accordance with their ideological convictions when the cost of doing so is low than when the cost is high. This prediction is subject to rejection by empirical evidence and thus avoids Machan's methodological concern.