The problem is that "rational" is taken as the highest good by some people, and a key part of their identities.
Unfortunately these people have mammalian brains, which are a prefrontal cortex sitting on top of an antediluvian limbic system. To pretend that you are rational and not emotional is to launch vigorously down the path of self-deception.
It inevitably follows that one's post-rationalisation becomes both deep-rooted and hidden from one's own view. To roughly paraphrase tfa, you'll cherry-pick facts and apply narrow logic. Worse, you'll be bolstered by the unshakeable conviction that you are completely logical. Then you'll become extremely passionate in defense of your beliefs. The irony...
It is excellent to strive for rationality, just as long as one keeps one's own fallibility in mind. That implies self-knowledge. You can't reach the top of Maslow's pyramid without self-knowledge; we should teach techniques to cultivate it in schools.