All people are free thinkers. That’s the nature of the human brain.
However, it can occur that ideology is more powerful than objective reason. The brain must have a structure via society and culture; and this structure will determine the thoughts of folk.
I’ve known born-again Christians who are open to listening and accepting others; Muslim, atheist, Jewish, etc. It’s not the religious beliefs that stop free thinking. It’s the individual who chooses to close up and think they know what’s true.
You can believe in something adamantly, because our brain has evolved to do that. Our hunter-gatherer ancestors required this trait of belief both for rationalizing the environment as well as solidifying social bonds. When your dad tells you something, you believe it and at the same time freely think what else could be. In our modern era of information, a religious believer is faced with apparent contradictions more confounding than the ancient humans. With great information comes great questioning. The proper religious person will indeed ask why God made the world this way. Again, that’s the human nature of the the complex brain.