The Sociology of religion? I thought that the problem with challenging religion was that it's irrationality may not just be vested in it's beliefs but also by the fact that various self interested parties depend on it. And these interests defend it against those that may challenge it or offer an alternative. From sociology, it may be obvious to observe that human beings form groups and they often have internal structures including an authority figure (though not necessarily so). The interest of the individual depends on their relation to that group, often their survival. Though the Roman Catholic Church in Europe has weakened since medieval times (I assume), it seemed as though during that period it was one of the most important economic, social and political organisation in Europe. Secular authorities executed opostates and heretics and prosecuted wars at the instruction of the Church. I wonder if you were almost obliged to have some relation to it.
We think of our forebears, in the absence of scientific knowledge, to be ignorant and to believe anything that is said particularly by an authority. But, I wonder whether this is only partially true. Perhaps all possible opinion existed within a human population but, their frequency may have varied and may not necessarily have been expressed or recorded. Apostates and heretics were said to be executed by burning at the stake by order of the Catholic Church. It may therefore not be sensible to have expressed a personal view and they may not have been recorded. Still, is it possible that a trading society would have been inclined to scepticism since they would have had to look at what another is selling with a degree of criticality. Would they not apply this to the teachings of the religious authorities. Perhaps this results in pragmatic conformism rather than blind faith.
Is religion in itself a cause of conflict? The twentieth century seemed to be based around conflict of various groups on the basis of ideology (though they also seem to have existed between pre-existing nation states). Is the conflict simply between groups of people as one form of possible relationship rather than the basis for the group itself? I.e. established groups of people meeting each other, I assume, have a finite number of possible relations such as coexistence, isolation, integration, assimilation by one group of another, to conquer or annihilation of one group by another (presumably numerous others). When one group challenges another, the people inside that group do not know what such a change would bring and what place they would have in a new group of both original groups due to say being conquered (or at least some relation that puts their position at risk) . This could also take the form of a pre-emptive strike or recruitment such as conversion of the heathens/pagans etc.
As perhaps an example of a conflict born of a social order issue rather than belief in themselves I would suggest considering the amount of effort expended by the Catholic doctors. Their activity, I think, has been decried as intellectually unproductive and characterised as 'counting how many angels can sit on the head of a pin'. But if failure to create an elaborate and thoroughly explored set of beliefs was not done, differences found in interpretation, etc., could form the basis of a break off group or schism dividing the church, reducing its authority, putting those positions at risk and even violent conflict for dominance. So, in fact, what seems trivial matter here and now, in the context of a social order, could have been matter of grave seriousness for the social order of the society the church existed in.
Defence of false beliefs using often poor arguments and circular reasoning could just be a person's way of defending their self interest at all cost including at the expense of facts and reason.