Harry Potter and the Methods of Rationality finished today

That said, it is rare that a work of fanfiction manages to be a legitimate deviation and self-contained work that both comments and reflects upon its originator usefully. Generally speaking, I prefer to give all fiction the benefit of the doubt: whatever its failures, it is hard to ignore that it was successfully written and as someone who has tried my hand at it, I know firsthand the challenge overcome. There's a "Man in the Arena" quote insertion that belongs here. I did find it to be a good and engaging story, though, if painfully in need of an editor, which is not a unique remark in the land of fanfiction.

If you want to really have fun, compare HPMOR with the Left Behind series, which qualifies as fanfiction as much as anything. There are probably some fascinating parallels to be found with their relationship to their original works and author intentions and the like. You can find a much higher quality counterpart to su3su2u1 in Fred Clark's Slacktivist blog, which dissects it on a page-by-hilarious-page basis.

In my (admittedly extremely limited) exposure to him as a person through videos of his talks and some of his transhumanist writing, I didn't really get the impression that he's anything but a very nice and gifted person. So I think this practice of judging or dismissing entire lives by applying a simplistic theme is an antipattern, and this is true here, too. There's a reason why ad hominem attacks are generally frowned-upon.

Yes, I personally found the certainty with which several conclusions are asserted as universal truths on LessWrong in general offputting at times, especially when used in conjunction with the Rationality label, insidiously implying any other analyses of the subject matter would be inherently irrational.

However, some subjectively bogus tenets notwithstanding, I still think it's a valiant and intellectually stimulating attempt at building a new philosophical framework which could potentially keep up with science and future human development. At the very least LessWrong Rationality is a good basis for an ongoing discourse on the subject, and at its best it demonstrates a unique exploration of ethics and, indeed, rationality.

You may argue most or even all of this framework is lifted from earlier philosophical and scientific achievements, but in some areas standing on the shoulders of giants is actually a good sign you're in the right place.

Here's a key passage: "Observational vocabulary is not a vocabulary one could use though one used no other. Non-inferential reports of the results of observation do not form an autonomous stratum of language. In particular, when we look at what one must do to count as making a non-inferential report, we see that that is not a practice one could engage in except in the context of inferential practices of using those observations as premises from which to draw inferential conclusions, as reasons for making judgments and undertaking commitments that are not themselves observations. The contribution to this argument of Sellars’s inferential functionalism about semantics lies in underwriting the claim that for any judgment, claim, or belief to be cognitively, conceptually, or epistemically significant, for it to be a potential bit of knowledge or evidence, to be a sapient state or status, it must be able to play a distinctive role in reasoning: it must be able to serve as a reason for further judgments, claims, or beliefs, hence as a premise from which they can be inferred. That role in reasoning, in particular, what those judgments, claims, or beliefs can serve as reasons or evidence for, is an essential, and not just an accidental component of their having the semantic content that they do."

EDIT2: This might be a more helpful explanation. Elsewhere, Brandom elaborates on this view by redefining beliefs as commitments. A commitment entails some other commitments, and is mutually incompatible with others. For example, if I believe that I'm eating an apple, this entails the belief that I'm eating a fruit. It's mutually incompatible with the belief that I'm eating a squid. It also entails that I believe things I might not even know about the apple, such as the chemical formulas for the various sugars I'm eating. The point is, if I play the game of reasoning correctly--mostly by dispensing with mutually incompatible commitments when they arise--others (e.g. botanists, chemists) can hold me accountable for all the correct beliefs about the apple. The "content" of the apple, for me, is nothing other than the series of moves I make in this game.

EDIT1: You should also read rpedroso's comment, which does a great job exploring the many alternatives that arose after empiricism reached its impasse.

1: http://ceur-ws.org/Vol-444/paper01.pdf

2: Not only empiricists, but possibly Kant on a very straightforward reading--although Brandom has a very different reading of Kant.

That doesn't mean everything he writes stands up, but he's smart enough that you have to think a while about what might be wrong with his arguments, and that's entertainment enough.