It's not just relevant because Yudkowsky wrote it, it's relevant because it essentially serves as Rationalism's "Torah".
Is it perhaps possible one of these is not like the others?
I've seen Rationalists defend it against very fair and accurate criticisms (see this whole thread for some of those), completely failing to recognize the complaints and objections are often legitimate.
I believe I've seen people cite it as the thing that brought them into the Rationalist community.
It's not uncommon to see people quote it in varying capacities - as a reminder of what "good rationality" looks like, as a cultural shibboleth, as a criticism of an idea they disagree with, and more. As an ex-evangelical who's read the Protestant Bible well over five times, this behavioral pattern looks very, very familiar.
I'm not going to spend the hours digging to find actual evidence I'm correct, and it's possible I'm being unfair and misremembering. I'm just a guy on the Internet - don't take this as anything other than "Here's my recollection. Take it for what it's worth."
The label of "Torah" did not strike me as wrong, though.
The rest of it, not so much. Of course I've seen people say positive things about it, and I've seen people say more positive things about it than I think it deserves. But that, too, is very different from treating it as a holy text; surely the same is true of pretty much anything that a lot of people have read and liked.
I just did a search for comments on LessWrong in the last year that contain the string "HPMOR" -- unsurprisingly there are hundreds of them, so I looked at the first few pages of results. I found a fair amount of "X reminded me of Y in HPMOR" but nothing that looked (to me; of course I might have blind spots) as if the thing was being treated like sacred scripture. E.g., no instances of "you say X, but HPMOR says Y, so obviously you're wrong" or the like.
It feels to me less like the way Christians relate to the Bible and more like the way they relate to, say, the works of C S Lewis. A shared bit of culture that can be referred to; something a lot of them like; in some cases the thing that brought them "into the fold".
Maybe I've just failed to notice. Maybe I've noticed in the past but forgotten. (I'm pretty good at forgetting things.) Maybe the search I just did was the wrong one -- e.g., maybe for some reason rationalists treating HPMOR as scripture tend not to call it "HPMOR" while doing so. But so far I remain unconvinced.
I'm not sure that's the case here, because rationalist fanfics tend to instead try to tear down the world as illogical.
Example for Harry Potter and this fanfic. In Harry Potter magical currency is made of precious metals and there are bronze coints, silver coins and gold coins. And they have fixed exchange rate.
"But wait!", notices the rationalist. "Since those coins could theoretically be melted down, and rates for those metals on exchange is different I could make infinite money glitch and crash the economy. Those wizards are so dumb, haha, for thousands of years they never figured out the basic logic."
Congratulations you found an economical inconsistency in a children's book. Your next period is boxing against kindergartners.
In my mind if you were a fan of original work, you would not be doing this. You could find different explanation that does not try to paint the world as stupid. Simplest being https://xkcd.com/1494/