I think the issue with the community is they take their eccentric beliefs as being gospel truths which can lead to truly unhinged and irrational beliefs and actions (see: the Zizians).
That's what can make the rationalist movement feel more like a religious cult and less like a bunch of eccentrics. As an outsider looking in, it seems like the entire movement is filled with just accepting priors with very little evidence for why those priors should be accepted.
>the issue with the community is they take their eccentric beliefs as being gospel truths
I am genuinely curious where you get that impression. The central element to the whole thing is that people should be willing to question their own beliefs and change their mind based on the data.
If there is anything that turns rationalists into eccentrics, I it is being overly open to new ideas or beliefs.
Consider a community filled with 100 people; 95 of them who don't take their eccentric beliefs as gospel truths and 5 who do. Those 5 will inevitably become the public face of the community when they make the news. However there is very little that the 95 could have done to stop them.