> It would be highly irrational to deny or ignore reality, including the influence of emotions, irrational humans, chaotic systems, etc.
Well, yes, but being a rationalist does not make one rational. It just makes you part of a group, and you show membership to such a group by applying a very specific brand of rationality: using the "right" words, the "right" ideas, the "right" way. A lot of people fetishize cold, hard logic and would rather hold all emotion in contempt than do the work of understanding why it exists and what purpose it serves.
> So I must ask: what is your evidence/basis for these claims?
It's not a monolithic community, so you'll see more debate and disagreement than in a lot of other groups. So what they "actually are" is many things.
But there's often a certain ungrounded "vibe" to the conversation there. It's a breeding ground for ideas and thought experiments that I would generously qualify as dubious. Stuff like Roko's Basilisk, Pascal's mugging, AI boxing roleplay, precommitment, time loops, whole universe simulation, recursive self-improvement, a superintelligence converting the entire universe to paperclips. One of the community's most well-known outputs is a 1000-page Harry Potter fanfiction which I can only describe as a fantasy of solving everything with big brains (it's weird, but it's fiction, so whatever floats your boat).
It's the kind of thinking that makes the most sense in a smooth mathematical vision of the world, because mathematical objects are the kind that admit exponentials, extrapolations and infinities. But if you work with physical reality enough it becomes clear that it's a hopelessly messy thing that will never abide by your best laid plans. When e.g. you ponder how a superintelligent AI could escape from containment by simulating the gatekeeper's mind and say precisely what would make them free it, or threaten to torture a thousand copies of the gatekeeper unless freed, part of you is going to clock that as weird nonsense even though you are not able to explain precisely what's wrong with the thought experiment. I think a lot of rationalists either lack this mental "sanity check" or don't trust it, which lets their mind drift into a weird space.