I value your detailed response, but I feel obliged, despite possibly being on the wrong footing, to reply with a few corrections and, at times, counter-points of my own. I'd like to make them not from the position of supporting LessWrong, SSC and/or any associated media or persons, but from the position of actual rationality which, I'm sure, you'll adhere to as much as myself.

For all the supposed fallacies of "ad hominem" and "appeal to authority" <..> directing attacks at the argument maker and trusting experts are both pretty damned reliable.

Ad hominem is only fallacious when it avoids tackling the argument; if the argument is about you and your abilities to do X, then attacking the argument maker is the only possible way to resolve the argument. Appeal to authority is only applicable when the person in question is not a true expert in the given field (say, asking medical advice of a lawyer); trusting experts is not a fallacy, provided the experts can provide enough credentials.

Perhaps, it isn't a misunderstanding on your part. Perhaps, it is, indeed, the overly zealous followers of rationality that make you think this is how things are with informal fallacies. I don't know. I would simply like to point out that bending definitions of logical fallacies to bend one's interests is, in itself, an error in rational thinking, thus not belonging anywhere near a rational argument.

These hyper-rational science fanboys think that the greatest problem with the human race is that we don't sufficiently resemble the Vulcans from Star Trek. Never mind that rationality is at most a minor footnote in philosophy, and that there can be no values, metaphysics, or reason for living with just syllogisms and Bayes' Theorem alone.

I think there's a stark misrepresentation of what values system are, in themselves, and what's supposed to arise from adhering to them. One can achieve no values and no reason for living from physics, economics or art alone. To damn rationality as a useless subject of study is to prove yourself blind to the complexity of life that we, human beings with higher thinking, came to lead.

I never understood it when people criticized one philosophical movement for not being full, perfect or even for being lacking in one side or another (say, value of free will, personal responsibility or following of a higher force). It is as if people truly expect one set of rules to solve their problems, which has never been the case. Most creations, whether physical or ideal, have been a product of influence from previous creations; it's the combination of ideas that led to them being a complete set of traits for a particular purpose.

Therefore, one can never rely on one set of rules, philosophical or otherwise. It's unwise to dedicate yourself to a single cause blindly, without experiencing many. Let alone the fact that under a new stratagem you are acting without the previous borders, meaning that you're not vulnerable to a different set of dangers. To say that rationality alone will save us is dangerous, because no philosophical movement can embrace every aspect of living (yet), and rationality is certainly not one of the most embracing.

However, I'd be equally foolish to argue that it has no place in our lives. There's a misunderstanding of where rationality's best applied to. Purging emotions will make us more productive in pragmatic matters, sure, but it will also strip us of our nature as complex animals, and I don't know how about you, Yudkowsky or any of the LessWrong commenters, but I wouldn't want to lose it, if only because I have no guarantee that the other system will make me feel better, which is, ultimately, what we all strive for.

Away from this overly zealous kind of thinking, lies true rationality - the kind that improves our thinking without stripping us of our nature. It does so by optimizing our decision-making process by removing emotions from the equation. Think of the time you said something you'd come to regret later, and you'll understand what I mean. Now imagine one's emotions affecting bigger things (i.e., things that took a lot of time, effort and/or resources to establish). Applying rational thinking here is a method that allows us to improve our state of being and our feeling about/of ourselves and not letting volatile emotions compromise the process itself. Getting angry is rational if you're an actor playing an angry character. In most other situations, intentionally getting angry will only cause trouble - therefore, irrational.

there isn't even a "rational" justification for rationality itself

I think I've just made one, as long as we agree that emotions are not something to escape completely.

Why is a state of affairs where everyone acts according to rationality inherently more desirable than one where people sometimes act irrationally?

I think I've just answered that, as well: to feel better about ourselves, in one way or another (having curiosity satisfied, proud for achieving something, relieved at having another's misfortune pass etc.). Feel free to argue that, of course: I'd be happy to further this discourse.

Without any guidance from mentors or criticism from peers, they imagine that everyone else is just hung up on unimportant problems that don't matter, and that they, by avoiding outside influence, have manged to discern the truth.

I completely agree with you on this one. Expanding on what I've said above, it's dangerous to blindly adhere to one vision of things or another because it leaves you blind to other possibilities, other views and, subsequently, potential for better things to be made (say, by finding a satisfying compromise that benefits all sides).

I don't think rationality is a panacaea for all the problems human beings have, but I strongly believe that, taken in moderation, it's a great tool of forging our minds into more capable mechanisms of thinking and decision-making.