Mike Clawson, posting on Friendly Atheist (one of my favorite blogs), reported on a series of articles suggesting that women are more religious than men because they have been conditioned, by both evolution and culture, to be "more emotional or social, and therefore less rational." The discussion going on at FA about what factors are causing the disparity between men and women are very interesting; more interesting, in fact, than what I could write on the issue myself. However, I think the wording "more emotional or social, and therefore less rational" needs to be discussed, because it propagates a myth that because women are more emotional than men, it follows they they must be less rational.
In general, there is a general misconception that being rational means relying on "cold, hard logic" and completely disregarding other facets of our world, such as human emotions. A good example of this is the Straw Vulcan trope television and movies use so often, where rational "geniuses" become dumbfounded by simple human emotions. It is assumed that reason cannot coexist with emotional acuity. This overused character trait seems to come from a mistaken view of rationality, and perpetuates this stereotype, creating a feedback loop of bad press for logic and reason.
This, of course, is a completely mistaken view of rational thought. In many situations, emotional reactions play an important role in our decisions, particularly concerning ethics. For example, I am a monogamous relationship with my fiancée, and would never cheat on her with another woman. If emotional responses are left out of this, there doesn't appear to be a rational reason for this. It doesn't physically hurt anyone if I were to sleep with someone else.* I am still capable of holding the same relationship with my fiancée after the affair (assuming emotional responses don't factor into my abilities). It doesn't seem to hold that having sex with another woman is inherently immoral.
But emotions are the key. My fiancée would possibly be hurt, angry or jealous. I would feel guilt and shame. This is why we've agreed on a monogamous relationship in the first place. These feelings are not desirable, and thus it is rational to avoid them.
Being more in-tune to others' emotional states, as well as one's own, helps us make better-informed decisions, which by definition are more rational, not less. Although its unclear how true the stereotype that women are more emotionally capable than men is, it has no bearing on the ability of either to think critically. This non-sequitur is a bad argument, and it propagates a sexist idea that women are less capable of being rational than men.
* One might argue that the risk of STDs or pregnancy is a valid consideration, but even if there were a way to guarantee these won't occur, most would argue its still irrational to think its OK to cheat, solely due to the emotional responses of those involved.