Why is rationality so often associated with a lack of emotion?
I can think of several good reasons, actually. Rationalism deemphasizes emotion as a way of gaining or interpreting knowledge. If you use emotions to determine truth, they can easily lead you astray by biasing your judgments. For example, if you're angry at a person, you're more likely to think them guilty. If you're happy with someone, it becomes as easy to miss their flaws as it is to miss one's own. Rationality doesn't stop you from feeling emotions, but it stops you from using them to twist reality.
The end result: rationalism diminishes the role of emotion. I'd like to think that it only diminishes the bad parts of emotion, but people are not perfect, and emotions can be messy. It's only inevitable that we throw a little of the baby out with the bathwater.
Another reason that people might think rationality and emotion can't mix is because of the sort of people who espouse logic and reason.
Well, first there's me. I bet I sound like a killjoy all the time. This, I claim, is an illusion. Not that I'm secretly the touchy-feely type or anything. It's just that this here is a medium in which the only emotion that can reliably be conveyed is anger. Thus the need for emoticons. It's said that eyes are windows to the soul, so I suggest staring into that colon until you know me. :-0
And then there's everyone else. I am a bad judge of stereotypes, but I suspect that people see rationalists as arrogant. Uh, maybe so. But I don't think arrogance is inherent to rationalism. Why should rationalists be any more arrogant than anyone else? Is it because rationalists think logic makes everything certain? If so, then they're just plain wrong. Is it because they believe they can judge some claims to be better than others? Then what's everyone else, a hardcore postmodernist?
But of course, arrogance is an emotion too. Arrogance can twist a person's perception of reality just as much as any other emotion. That should have been a no-brainer; not every emotion is the feel-good kind. Sure, there's love, hope, and happiness, but there's also anger, shame, and arrogance. When it comes to discussions, debates, or arguments--all of which are common places to encounter rationalists--"high emotional content" means an abundance of the negative emotions, not the positive ones. This doesn't indicate a lack of regard for the opponent's feelings, it involves a purposeful manipulation of the opponent's feelings.
I see it as a win-win situation. By avoiding arrogance, I avoid a potential source of bias and show respect for others. So forgive me if I am a little unfeeling in other respects as well.