At least one cult originates from the Rationalist movement, the Zizians [1]. A cult that straight up murdered at least four people. And while the Zizian belief system is certainly more extreme then mainstream Rationalist beliefs, it's not that much more extreme.

For more info, the Behind the Bastards podcast [2] did a pretty good series on how the Zizians sprung up out of the Bay area Rationalist scene. I'd highly recommend giving it a listen if you want a non-rationalist perspective on the Rationalist movement.

[1]: https://en.wikipedia.org/wiki/Zizians [2]: https://www.iheart.com/podcast/105-behind-the-bastards-29236...