IQ is a part of it. Oddly, it tends to be people at both the upper and lower ends of the scale who tend to see through the bullshit society imposes on us all. At the upper end we have people who are able to look at all the explanations and excuses for why "this is just so", and reject it all as illogical superstition. At the lower end, they never begin to understand the morass of superstitious explanations and circumlocutions, and just compare what is said with what they know - and find the explanations lacking.

But, more important than intelligence is a willingness to go against the grain. Human beings have a deep need to belong to a group, and they learn early on that they must suscribe to certain shared values in order to belong to a group. Those who differ in many ways from the norm are more likely to question those values in the first place, and those whose differences are so great that they cannot help but be excluded are forced to question those values. Both high and low intelligence are such factors, but are not the only factors. Once a person has concluded that one social value is wrong, they are more likely to start questioning other values, and the more they decide are wrong, the more likely there is to be a snowball effect.