That's not obvious to me at all... my rough (highly uninformed) model of how cult initiations work is that you get sucked in to a situation (e.g. Scientology "stress testing" or similar) where you're forced to either not conform or join the cult. (Also fits my (very limited) observation of fraternity initiations.)

Entirely possible. I'm not sure the fraternity analogy holds water; at many colleges I would expect the decision to seek out a fraternity (as opposed to the decision to join one) to be at least partially motivated by obtaining higher status, whereas joining a cult generally only gets you higher status among existing cult members. I'm working primarily off of Cultish Countercultishness, in particular this part:

There's a legitimate reason to be less fearful of Libertarianism than of a flying-saucer cult, because Libertarians don't have a reputation for employing sleep deprivation to convert people. But cryonicists don't have a reputation for using sleep deprivation, either. So why be any more worried about having your head frozen after you stop breathing?

I suspect that the nervousness is not the fear of believing falsely, or the fear of physical harm. It is the fear of lonely dissent. The nervous feeling that subjects get in Asch's conformity experiment, when all the other subjects (actually confederates) say one after another that line C is the same size as line X, and it looks to the subject like line B is the same size as line X. The fear of leaving the pack.

Your second point is also fair. What I think is implausible is that everyone who self-identifies as an intelligent nerd is actually intelligent. Maybe they only like thinking about nerdy topics but aren't good at it and tell themselves a story about how they're intelligent to fit in and maintain their self-image (being a dumb nerd sounds awful).

That's not obvious to me at all... my rough (highly uninformed) model of how cult initiations work is that you get sucked in to a situation (e.g. Scientology "stress testing" or similar) where you're forced to either not conform or join the cult. (Also fits my (very limited) observation of fraternity initiations.)

Also keep in mind that people who join cults are not a random sample of the population. It is generally believed that people who join cults are usually in some way social outcasts to begin with. Cults offer them the possibility of being part of a close-knit community. Traditional religions also offer that, but to a lesser extent.

Just because a story is flattering to your group doesn't mean it's false. The research I've seen on the usefulness of high IQ for achieving desirable life outcomes has been pretty positive.

References?

AFAIK, it is well established that IQ positively correlates with many performance metrics for levels of IQ around and below the average, while the correlation for above average IQ is more dubious. In fact, IQ tests were originally designed to detect underperforming individuals.

The correlation between an high IQ and being a "nerd" is also debatable, while, at least in some circles, nerds may have an high IQ, it doesn't follow that many high-IQ people are nerds. Also note that the whole concept of being a "nerd" migh be largely the effect of conformity biases.