Let's assume their are gradations of belief ala Dawkins
1. Strong theist. 100 per cent probability of God. In the words of C.G. Jung: "I do not believe, I know."
2. De facto theist. Very high probability but short of 100 per cent. "I don't know for certain, but I strongly believe in God and live my life on the assumption that he is there."
3. Leaning towards theism. Higher than 50 per cent but not very high. "I am very uncertain, but I am inclined to believe in God."
4. Completely impartial. Exactly 50 per cent. "God's existence and non-existence are exactly equiprobable."
5. Leaning towards atheism. Lower than 50 per cent but not very low. "I do not know whether God exists but I'm inclined to be skeptical."
6. De facto atheist. Very low probability, but short of zero. "I don't know for certain but I think God is very improbable, and I live my life on the assumption that he is not there."
7. Strong atheist. "I know there is no God, with the same conviction as Jung knows there is one."
Editorial note: I particularly like seven point scales because it allows shading between the neutral 4 position and the extremes.
Ignore for now the infinitely fine gradations that exist between the major points, the "Strong theist" and "De facto theist" positions may argue for a more literal interpretation of the Bible, whereas the "Strong atheist" and "De facto atheist" will refute the same. Referring to these positions as 1,2,6 & 7 from here on, I presume that having a strong position on something exposes one to, or entails, a confirmation bias towards that position and anything resembling evidence that supports it. If a person is also outspoken about their position, it also makes sense that the person becomes entrenched, because there is now some ego tied up in having, and publicly espousing the position.
We all want to matter. we want to be important to one person (your spouse, for instance) - and usually you want to matter to your wider family, at work, in circles of friends, and sometimes outward into the community and the larger world.
Arguing vehemently for or against theism speaks to the arguer having and displaying that need to be important. It also, coincidentally, puts one in the position of adapting to the view that 1) the world is a static place where life, death, judgement, heaven and hell are real and inevitable; or contradictorily, the world is a dynamic place where what we know is replaced with more accurate knowledge when what was previously acknowledged is either falsified and replaced; or refined and elaborated upon.
This last little dichotomy, the apparent separation between a static and dynamic world view, is something I've observed over and over again as I engage in discourse about the Bible. It has opened a window into the "why" most 1s and some 2s are so resistant to the idea of evolution and express the need to "know" - and to criticize science because it doesn't know everything.
I don't know which comes first - the resistance to a dynamic world, or a belief in a world view that cannot accommodate change at the same rate that it occurs in real life.