Thinking too hard about anything will drive you insane but I think the real issue here is that rationalists simply over-estimate both the power of rational thought and their ability to do it. If you think of people who tend to make that kind of mistake you can see how you get a lot of crazy groups. I guess I'm a radical skeptic, secular humanist, utilitarianish sort of guy, but I'm not dumb enough to think throwing a…
The first is diffusion of power. Social media is powered by charisma, and while it is certainly true that personality-based cults are nothing new, the internet makes it way easier to form one. Contrast that with academic philosophy. People can have their own little fiefdoms, and there is certainly abuse of power, but rarely concentrated in such a way that you see within rationalist communities.
The second (and more idealistic) is that the discipline of Philosophy is rooted in the Platonic/Socratic notion that "I know that I know nothing." People in academic philosophy are on the whole happy to provide a gloss on a gloss on some important thinker, or some kind of incremental improvement over somebody else's theory. This makes it extremely boring, and yet, not nearly as susceptible to delusions of grandeur. True skepticism has to start with questioning one's self, but everybody seems to skip that part and go right to questioning everybody else.
Rationalists have basically reinvented academic philosophy from the ground up with none of the rigor, self-discipline, or joy. They mostly seem to dedicate their time to providing post-hoc justifications for the most banal unquestioned assumptions of their subset of contemporary society.