I think you hit nail on the head. It seems to me that LW represent bracketing by rationality—i.e. there’s lower limit below which you don’t find site interesting, there is the range where you see it as rationality community, and there’s upper limit above which you would see it as self important pompous fools being very wrong on some few topics and not interesting on other topics.
Dangerously wrong, even; the progress in computing technology leads to new cures to diseases, and misguided advocacy of great harm of such progress, done by people with no understanding of the limitations of computational processes in general (let alone ‘intelligent’ processes) is not unlike the anti-vaccination campaigning by people with no solid background in biochemistry. Donating for vaccine safety research performed by someone without solid background in biochemistry, is not only stupid, it will kill people. The computer science is no different now, that it is used for biochemical research. No honest moral individual can go ahead and speak of great harms of medically relevant technologies without first obtaining a very very solid background with solid understanding of the boring fundamentals, and with independent testing of oneself—to avoid self delusion—by doing something competitive in the field. Especially so when those concerns are not shared by the more educated or knowledgeable or accomplished individuals. The only way it could be honest is if one is to honestly believe oneself to be a lot, lot, lot smarter than the smartest people on Earth, and one can’t honestly believe such a thing without either accomplishing something impressive that great number of smartest people failed to accomplish, or being a fool.
Some of the rationality may to significant extent be a subset of standard, but it has important omissions—in the areas of game theory for instance—and much more importantly significant miss-application such as taking the theoretically ideal approaches given infinite computing power as the ideal, and seeing as the best try the approximations to them which are grossly sub-optimal on the limited hardware where different algorithms have to be employed instead. One has to also understand that in practice computations have cost, and any form of fuzzy reasoning (anything other than very well verified mathematical proof) accumulates errors with each step, regardless of whenever it is ‘biased’ or not.
Choosing such a source for self education is definitely not common. As is the undue focus on what is ‘wrong’ about thinking (e.g. lists of biases) rather than on more effective alternatives to biases; if you remove the biases that won’t in itself give you extra powers of rational thinking; your reasoning will be as sloppy as before and you’ll simply be wrong in an unusual way (for instance you’ll end up believing in unfalsifiable unjustified propositions other than God; it seems to me that this has occurred in practice)
edit: Note: he asked a question, I’m answering why it is seen as fringe, it may sound like unfair critique but I am just explaining what it looks like from outside. The world is not fair; if you use dense non-standard jargon, that raises the costs, and lowers the expected utility of reading what you wrote (because most people using non-standard jargon don’t really have anything new to say). Processing has non zero utility cost, that must be understood, if the mainstream rationalists don’t instantly see you as worth reading, they won’t read you, that’s only rational on their part. You must allow for other agents to act rationally. It is not always rational to even read an argument.
Actually, given that one could only read some small fraction of rationality related material, it is irrational to read anything but known best material, where you have some assurance that the authors have good understanding of the topic, including those parts that are not exciting, or seem too elementary, or go counter to the optimism—the sort of assurance you get when the authors of the material have advanced degrees.
edit: formatting, somewhat expanded.