I think there's a simpler foundational answer as to why Rationalism seems to produce cults or cult-adjacent groups. It's perhaps not a comfortable one. Autistic people are overrepresented in rationalist spheres. While some traits of autism are protective against vulnerability to cults, others make autistics more vulnerable. Especially when there are risk amplifiers like trauma history (from what I know, the Zizians, for example, are quite traumatized individuals).

I say this because I've been around the community for a while, am very interested in cults (in an academic sense), and am autistic myself.

To be clear, having trauma doesn't make murdering people an okay thing to do. The Zizians are, in my opinion, batshit.