I have for a long time been interested in what motivates outspoken theists. Using Twitter has enabled me to interact with some of them, and observe some of their thinking in their responses to my tweets. In terms of their motivation, I am not much wiser, but I may now have some inkling of the positions that they adopt when debating with atheists.
Overview of Evidence
The evidence presented here is far from being rigorous, but it may provide pointers to other researchers who are interested in this question. It strikes me that there are two themes which are the fall-back of die-hard theists when confronted by atheists’ questions: “The Bible is truth” and “Truth is absolute”, and that both of these positions may underpin the responses which they give to atheists.
If we look the discussion from the point of view of theists, it is perfectly reasonable in their eyes to use the Bible as a means of dismissing the arguments put forward by atheists. They can, for example, claim that any atheist who questions the validity of the Bible will suffer eternal torment in Hell, because this is what the Bible tells them.
Moving in a context slightly wider than just the Bible, it also legitimises (in the eyes of theists) such positions as “The soul is what enters the body at birth, and leaves it at death” (Saivism, twitter @OmNamaShivayaa) without offering anything further, thus side-stepping any question of testability.
It also explains the assertion that the spiritual world can only be glimpsed (Stu Pedasso, twitter @mr_stinkynuts), and that any questions about how that world can be measured and tested are treated with contempt.
It would seem that such theists regard their own preferred religious text to the exclusion of all else. By way of illustration, the Bible presents the virgin birth as a fact, while any gynecologist who has bothered to think the matter through will tell you that it is a physical impossibility. (I expect that the merry band of theists will attack my argument on the basis of the immediately preceding sentence.) Thus we have a group of people who are desirous of accepting a single source of evidence to the exclusion of all other sources. This would motivate such statements as made by theists in their fall-back position: they do not feel the need to defend such bald assertions.
I must confess that I find such a position to be puzzling in the extreme.
It is at this point that I must leave it to others to put forward their own ideas about what motivates such theists, and to thank them in advance for their efforts.