Looking at this topic more broadly than solely in terms of HPMOR and it’s reviews, I would argue that for many people their exposure to the concept of rationality is predominantly made up of half rationalists.
Rationality is hard. It gives us tools that allow us to update old preconceptions of the world. However in practice we will often fail in our rationality due to insufficient information or other cognitive limits while still identifying our actions as being superior due to rational principles. It is very off putting to see others claiming superiority yet still be full of flaws in reasoning due to bounded rationality. From your perspective you might clearly see a flaw in their reasoning, perhaps one you can’t communicate well, even if from their perspective they have applied rationality.
This creates cognitive dissonance for accepting the idea that rationalism leads to better reasoning.
EY wrote a bit about the dangerous of being half a rationalist within the body of this post if you want to continue this train of thought.
I’ve also went from a steady 23 total karma all in dead posts from a couple of weeks ago, and went down to 14 after posting this. I’m still rather new here, but I do remember reading that downvote stalking had become an issue in the past. Did LW ever resolve any policies to help combat that?