A response from an egoist perspective:
The more influence your thought process and decisions have, the more important it is that you're rationalist.
A professional and popular mixed martial artist must make many rational decisions, but his profession and popularity are more dependent on his physical strength, speed and fighter's heart. A professional and popular fashion model must make many rational decisions, but her profession and popularity are more dependent on her physical beauty and social charm. Some people are born with the potential for conventional physical strength and beauty and many are not. This is relevant because to say the punch of a fighter or the flashing smile of a model are also rational is to say either (a) some people cannot be rational or (b) everything is equally rational, 'ultimately.'
The more influential you are, the more your decisions have potential to screw over other people.
For a tyrant, or a spy, or a propagandist, or a soldier, screwing over other people is making decisions and influencing people. Rationality is as good for making other people suffer as it is for making other people prosper.
So rationality scales upward: the more influential someone is, the more important is it they're rationalists. Neglecting this can have bad consequences.
The more important to what person it is they're rationalist? To the rational agent, or to other people? It might be entirely rational to screw over other people. Fun, even.
I've read about a quarter of the sequences, but I'm not sure if this topic has been addressed on LessWrong before. If it has, let me know.
The Upward Scaling Importance of Rationality goes like this:
The more influence your thought process and decisions have, the more important it is that you're rationalist. In the grand scheme of things, it is relatively unimportant that a barback at a restaurant is a rationalist, and I say this having done that. It is extremely important that a leader of a highly influential company, or a president of a university or country is a rationalist. Their decisions affect thousands if not millions of people.
The more influential you are, the more your decisions have potential to screw over other people. Influence doesn't necessarily have to be in a management position: elementary school teachers and police officers are highly influential, even though they aren't in control of an organization. Influence can even be by virtue of the people you reach out to. A famous person with a large fanbase or a parent of a child prodigy, both have the capacity to influence the world with their decisions.
Though arguably, this can be extended to anyone who votes.
So rationality scales upward: the more influential someone is, the more important is it they're rationalists. Neglecting this can have bad consequences.