"Rationalist" just sounds like people calling themselves smart.
There's a little AI skepticism on HN, but not a ton. When ChatGPT 3 and 3.5 came out, most of the comments were remarking how well it can write code.
No, it's not just people calling themselves smart, it is a specific philosophy of how to think. Whether you think that philosophy works or not is another matter.
IMO it has its flaws but is far superior to vibes-based hot takes you see on HN.