the natural man doesn't really understand the Bible (1 Cor 2:14).
I think that unbelievers have a more objective perspective of what the Bible says and are therefore the best judges of what its message is. The unbeliever can look at a vague passage and say that it has no clear meaning as the Christians debate among themselves about which of them has the correct interpretation of what is essentially poetry.
The unbeliever can see an example of moral or intellectual failure by the deity and call it that, whereas the believer must sanitize the passage and convert it into something moral or reasonable, or just shrug his shoulders and say that God;s infinite goodness and intelligence transcends our puny minds' ability to understand that what appears monstrous or absurd really isn';t in some inexplicable way.
Ask an unbeliever what the story of Job tells us, and he'll agree with just about every other unbeliever: It is the story of a capricious god unjustly toying with the life of a good man as a demonstration to a demon. That's simply not acceptable to anyone, so the believer adds to the story to make it more palatable. Maybe God was punishing Job for an unstated sin, or training him to be a better person, or whatever one can improvise to justify what is unjustifiable without the ad hoc, just-so explanation.