Thanks again for your fairness and hospitality at the Midtown Scholar debate last month. It was a pleasure for me as well! You’ll have to come out to NYC some time in the coming months so I can repay it.
So, with your assent, let’s table the debate about morality for now and turn to this question of how it is that people come to be religious.
To answer your question, I think that believers and skeptics tend to approach the question of God’s existence in different ways. As you say, most religious skeptics, like myself, treat this as an empirical question; and finding the evidence insufficient, we withhold belief. But I think few, if any, theists come at the question this same way. That would mean becoming a theist by way of investigating the evidence and deciding that it’s sufficient to support one particular conception of God while ruling out the others. I don’t think I’ve ever met a person who can credibly claim to have done that, and since you say that the Christian-specific conception has “irrationality written all over it”, I’d assume you agree.
In any case, I’m not sure if you meant your three possibilities to delineate thelogically possible routes to faith, or the means by which most people in fact arrive at faith. But in either case, I think you left out a fourth possibility, and I’d go so far as to say it’s the most common one: the route of tradition.
What I mean by this is that most people believe in God because it’s the belief held by most people in their cultural in-group, the one that defines their identity and differentiates them from outsiders, and it’s safest and easiest to go with the flow. In some societies this is backed up by ostracism, harassment or even severe legal punishments for nonbelievers and dissenters, but it’s not usually enforced so harshly. More often, it’s simply passed down as received wisdom, what everyone in our society knows, what makes us who we are. When a belief is woven into the culture like that, few people will even think to question it.