I think a large percentage of professed “believers” pretend to believe what they are taught because (1) they are lazy, (2) it’s socially convenient, and (3) hardline creeds of all types, Christian and non-Christian alike, come with a built-in paradigm that there is something wrong with you if you don’t at least pretend to swallow in their entirety the “truths” you are taught. I think, deep down, a large percentage of professed “believers” of such creeds, from fundamentalist Christianity to Mormonism, Scientology and beyond, don't actually believe what they pretend to believe. At some deep level, they strongly suspect it isn’t true – they may have a strong intuition of a spiritual realm, a supreme intelligence or even that Jesus specifically is the key, but deep down they know the creed they pretend to believe is a manmade thing and not the way the universe really works.
In regard to spiritual matters, where the Pope, Billy Graham and Deepak Chopra really "know" no more than you, me or Bozo the Clown, I have very consciously refused to accept anything I’ve been taught just because it was taught by some supposedly authoritative source. The one time I tried to be a good little sheep (in the Campus Crusade days of my youth), I don't think the experiment lasted more than a week or two. Over the decades I have formed my spiritual beliefs on the basis of a combination of life experience, observation, study and intuition (and perhaps revelation). If (but only if) these things tell me a teaching I encounter deserves to be regarded as authoritative, I'll fit it into my belief system. Ergo, I actually believe what I claim to believe and don’t have to live my life in a state of cognitive dissonance, pretending to believe things I intuitively know aren’t true. (I don't insist that what I believe is true, or that others believe it, but it is always my best current estimate of the Truth.) I truly believe a large percentage of those who cling to hardline creeds do live in a constant state of cognitive dissonance, even if they loudly deny it.
This isn't to say that living in a state of cognitive dissonance is necessarily bad. Whatever gets you through the night, as the song says. Some people are able to navigate life quite well by pretending to believe things they intuitively know aren't true, perhaps because pretending to believe provides an appealing social framework for their lives (church, friends, rituals, security, etc.) and they are able to keep a lid on their intuitive doubts. I happen to live in a heavily LDS area, and my sense is that I am surrounded by professed "believers" who have almost lobotomized themselves in order to avoid the cognitive dissonance that pretending to believe Mormonism would have to produce in anyone with at least one foot in reality; on the other hand, they seem to be generally happy zombies who exhibit many of the Christian virtues. However, I’ve always been more interested in the Truth, or as close to it as I can get in this lifetime, regardless of whether it is appealing or comforting or makes me popular.
Some people, of course, do the same hard digging I've done and find that their life experience, observation, study and intuition leads them to fundamentalist Christianity, Mormonism, Scientology or whatever. Good for them - they are true believers in those creeds, and I respect them. But I don't believe this is true of most professed "believers." My observation is that a very large percentage have opted for the easy way out for a variety of psychological and social reasons unrelated to whether what they pretend to believe is actually True. If there is such a thing as someone who genuinely believes what he or she has been taught merely because it has an ostensibly authoritative source (the Bible, the Pope, or whatever), this to me would be a very odd and pathetic human being. When it comes to spiritual Truths, where there is no such thing as "knowing" in the same way I "know" my Ford is in my garage, I think life is about learning, maturing and evolving, not "accepting what you're taught."
My response obviously goes beyond just the Bible or Christian doctrines. Even if I were just talking about "discerning" vs. "being taught" the truths of the Bible or of particular Christian doctrines, however, I'd say the same thing. What is true in Christianity is, for me, a product of my life experience, observation, study and intuition (and, I hope, revelation). This doesn't mean I ignore biblical scholars and decide for myself whether something is true or what it means. It means I read as widely as I can among biblical scholars of all types (the "study" element of my formula) and then filter what I have learned through my own life experience, observation and intuition (and, I hope, guidance from the Holy Spirit). I may end up believing precisely what Scholar X says, but not because he says it. It is the study and thinking that a large percentage of "believers" aren't willing to do, because it is extremely hard work and might lead them away from the comfort and security of the creed they pretend to believe.