In the free-thought community, religious folks especially those that lean towards the conservative position, have always been charged with the inability to think. Possessing closed minds, or choosing not to use it. This, most people in the free-thought community attribute to the religious indoctrination, which normally catches hold of one from childhood.
There is certainly no doubt that religion creates an environment where the believers’ ability to think is dampened as a child. You are taught not to question the Pastors,Priests, Imams, Rabbi, etc, the Bible, the Qur’aan etc. It is "blasphemous" to question God, they drilled these commands into children's heads. The freedom to think is further eradicated by, for instance, the religious hierarchy insist that one should have faith – blind faith that is; accepting the religious position without questioning its validity.
Indeed, for most of us, describing these religious people came from having conversational experience with them. You know, the Christian or Muslim friend you have that always engages you in a discussion in which you find yourself in an argument that takes you in a continuous circle with no exit point – (circular arguments). Well, here is a study that says what you may have thinking about you friend/s. Of course the study looks at Political Conservatism. However, Political Conservatives tend to also be Religious Conservatives. They are both directly related.
“…. recent studies linking conservatism to low intelligence and "low-effort" thinking”
“A study published in the journal "Psychological Science" showed that children who score low on intelligence tests gravitate toward socially conservative political views in adulthood--perhaps because conservative ideologies stress "structure and order" that make it easier to understand a complicated world.” (Source – Huff Post)
Not only does the study show that adult conservatives are the product of people who may have performed lower intelligence wise as a child but another study shows that they appear to also be "low-effort" thinkers.
“The authors test the hypothesis that low-effort thought promotes political conservatism. In Study 1, alcohol intoxication was measured among bar patrons; as blood alcohol level increased, so did political conservatism (controlling for sex, education, and political identification). In Study 2, participants under cognitive load reported more conservative attitudes than their no-load counterparts. In Study 3, time pressure increased participants’ endorsement of conservative terms. In Study 4, participants considering political terms in a cursory manner endorsed conservative terms more than those asked to cogitate; an indicator of effortful thought (recognition memory) partially mediated the relationship between processing effort and conservatism. Together these data suggest that political conservatism may be a process consequence of low-effort thought; when effortful, deliberate thought is disengaged, endorsement of conservative ideology increases.” (Source – Personality and Social Psychology Bulletin)
Indeed, religion loves "LOW-EFFORT" thinkers and people who don’t think at all. In fact, the Church father Thomas Aquinas defines the people who are willing to accept religious ideology without questioning as the most virtuous.