"How dreadful!" cried Lord Henry. "I can stand brute force, but brute reason is quite unbearable. There is something unfair about its use. It is hitting below the intellect." ~ Oscar Wilde - The picture of Dorian Gray
having them? because there are evolutionary reasons for that.
expressing them? built into a pack mentality.
now, to say that an emotion is reason to do something, on its own, is irrational, but not without merit in society-- therefore social instinct, the modern version of survival instinct, offers a reason to allow emotion free range.
the frustration NTs generally feel is because rationality doesn't work in controlling our emotions as well-- at least not for me. so... emotions are irrational the same way a person can be irrational: frustratingly ignorant of (or oblivious to) reason.
we have sayings to prove that this is a prevalent phenomenon. "love is blind": your lover is ugly, and you love him anyway; this is illogical, but emotions don't have to stand up to reason. everyone knows emotions CAN be irrational; that isn't to say that emotional people are too stupid to recognize logic. they just sometimes don't notice it or choose not to.
I think that my discomfort with emotions (and emotional people) is resultant from the fact that I don't understand emotions. I don't like things I don't get, and I damn sure don't like things that seem to distract from whatever the Big Picture is. I can read people fairly well. I can pretty quickly parse out someone's motivations, and make pretty accurate predictions on how they will behave. Other people in this thread have made reference to the theoretical purposes and uses of emotions as indicated by evolutionary biology, and I can get that. But really intense emotions in other people just make me feel helpless. I don't know what to say or do...can't wrap my head around it. The point is, really, that I don't like the mess of emotions. They throw my whole thing off.