To be fair, I do think that education and the trappings of expertise are overvalued, and that the same probably applies to general intelligence. These things certainly don't prevent people from arriving at wrong answers.
I'm not saying that the average cult member--and here I'm talking about actual cults, in the sense of being abusive and coercive and separatist, not NRMs in general--has good critical thinking skills. Obviously, there's something wrong there. I'm only saying that, from everything I've read, the typical member is above average on the IQ scale.
Trust me, there are plenty of high-IQ people who believe in absolute nonsense. It's not even rare.
I'd argue you were just fooled by them. Repetition, diligence and impression management can create quite the charming facade behind which not a single critical and original thought can be found.