Most people know, intuitively or explicitly, the difference between rationality and rationalizing: The first implies a careful consideration of as many likely possibilities as one can manage, and determining the best option for overall success and well-being. The second has to do more with justifying a pre-determined course of action, or (more simply put) giving reasons to do what we really want to do. There are a number of well-written posts on these two themes over at Less Wrong, so I won't add much more on the distinction between these two.
What I will note, however, is an observation regarding the presuppositions that are at work in our cultural conscientiousness (at least as I perceive it). By and large, we work with the assumption that the majority of people, especially people in power, are more or less rational. Sure, we recognize the ideologically-driven component of partisan politics (see, for example, the impasse on spending and debt at the national and state levels). When it comes to making decisions (even within a particular ideology), we assume that most people function day-to-day as rational beings. What's more, we take for granted that those whose job it is to think rationally and clearly—academics or judges, for example—actually do so.
Sooner or later, though, we're going to have to come to grips with this false assumption, this vestigial remainder of Enlightenment principles.