Rational choice theory is a powerful foundation for thinking about social behavior (at least in its moderate versions). People have beliefs and goals; they survey the environment of choice and they arrive at actions that are intelligently related to the achievement of their goals.
However, as an exclusive, abstract description of human behavior, rational choice theory confronts a few major problems. A minor problem is the fact that people do not always act deliberatively. They may act out of impulse, habit, or example -- without devoting the thought processes to their current choices that would be necessary in order to formulate a rational plan in the circumstances. This is a minor problem, because this behavior itself may be rational in the "satisficing" sense: the stakes may be so low that it doesn't make sense to commit time and energy to the task of calculating what the best overall solution to the problem is. (Shall I take the triple cappuccino or the iced mocha today?)
More challenging is a much more substantial fact about human action and choice: there is a powerful set of psychological imperatives and constraints that make certain choices psychologically impossible even when they are "goal-maximizing". Take food and clothing choices as examples: the fact that fish heads are perfectly nutritious and cheap will never induce most Americans to order them on the menu. The fact that a pair of Bermuda shorts is a perfectly suitable attire in some settings will not induce someone to wear them to a black tie gala in place of the tuxedo. It is as if the decision-making system is loaded with constraints of taste, preference, aversion, and norm that make some decisions simply impossible.
This fact might be described as the workings of "culture"; it might be categorized under the heading of "norms and values"; or it might be assigned to the "workings of personality and affect." But whatever description we offer, it is plainly a factor that needs to be incorporated into a full theory of human agency and choice.
It is not particularly difficult to model a "decision-making system" that incorporates the workings of tastes, aversions, and norms as well as goal-directed rationality. The more challenging task lies at the level of psychological theories of individual development (how does the individual acquire and incorporate these cultural and normative constraints?) and sociological theories of transmission of these sorts of constraints. What are the institutional and cultural mechanisms through which a system of tastes, aversions, and norms are transmitted throughout a group or population?
And, finally, there is the task for behavioral science of incorporating the empirical findings that this set of observations permits concerning the ways in which real agents process experience and arrive at decisions, into aggregate models of collective behavior. How should the abstract models of rational choice theory be extended to include these factors of affect, taste, and aversion? Are these non-rational factors so idiosyncratic that they cannot be incorporated into behavioral science? Or are there regularities at the level of individuals that permit aggregate consequences at the level of group behavior? (And is it possible that we have arrived here at the theoretical nexus of "marketing science" -- the discipline aimed most directly at understanding and controlling the behavior of groups of consumers?)
(An interesting edited volume by Lupia, McCubbins and Popkin explores some of these issues: Elements of Reason: Cognition, Choice, and the Bounds of Rationality .)