Pardon me while I think out loud. This is kind of half baked. If you see what I am trying to get at, and can say it better, please do so.
To know truth is perhaps the most illusive and yet most important things. Many of us have experienced the painful consequences of living under false assumptions. Unfortunately we are very limited in our ability to perceive and understand. Over thousands of years people have found that the best way to arrive at truth is to seek information, process that information using logic, validate that information and logic by seeking new data and ideas to test and validate against, and subjecting our conclusions to the scrutiny of our peers. The genuine truth seeker realizes this process will never end. We will never know all truth. The truth we know will always need to be refined in light of new facts.
As limited as we are and this process is, it still has had remarkeable success. It has brought us from cave dwelling, hunter-gatherers cowering from predators, to a complete domination of the planet. We have mapped the human genome. We have even "slipped the surly bonds of earth" to set foot on the moon. The power of truth and knowledge are unmistakeable.
One key flaw in this process is us. The simple fact is that two people can process the same information, use the identical system of logic (or so they think), and arrive at completely different conclusions. Human beings are simply incapable of being perfectly objective. This is the one thing that no person can deny, and is a key aspect of our fallibility. No matter how smart or knowledgeable we are, no person is immune from the need for self-delusion. It is the one common denominator we all share, and is implicit in all compromise. No person can ever be completely certain that they aren't biased in some hidden way to a certain conclusion.
So when we realize how difficult it is for us to understand and perceive reality, when we further realize how difficult it is for us to detach ourselves from what we want that reality to be, how completely obnoxious and laughable we find the jw who claims an absolute certainty in their beliefs, doctrine, and claim on "the truth".
Rather than constantly seeking new facts or ideas to refine their concept of truth, they build a wall and only dwell on the data or ideas that support their faith. They label any information or reasoning that challenges their beleifs as "apostate". They completely ignore the idea that their might be things they don't yet know, which they aren't even aware of, that might lead them to change their opinions.
But most importantly they refuse to admit that no matter how certain they are in the completeness of their knowledge and ideas, they themselves might be skewing the data to reach the conclusion they require. And when they claim absolute, complete certainty that they are right, you are wrong, they are actually saying that only you, and never they can be biased. They are denying that one common denominator we all share in our search for truth. They are denying their own humanity.
"doubts complete faith, and keep it from become fanaticism" -some smart Rabbi MJ quoted to me