How has nobody yet mentioned Confidence Levels Inside and Outside an Argument? Anyway, I take gjm's line on this: I should assign at least 5% probability that my reasoning for rejecting Christianity is invalid in some way that I'm unaware of, but that's different from a 5% probability that Christianity is true.
For one thing, my reasoning that Christianity is very likely false is essentially the same as my reasoning that other theisms are false, so at the very least a whole bunch of other religions get lumped into that same 5%. (That is, if Zeus exists, then my reasoning was just as wrong as if Yahweh exists.) Furthermore, there are other possibilities—such as that I'm mentally unbalanced and hallucinating my high intelligence, or that I'm a brain in a vat whose reasoning is being systematically tweaked for a mad scientific experiment—which don't seem all that correlated with whether Christianity is true or not.
Since in my case as well as yours, Christianity plays a unique role vis-a-vis other theisms, there is some justification for promoting it a bit within the space of "things that might actually be the case if my reasoning is bad" (in the same sense that a lottery winner might well consider it more likely than average that they're in a simulation). But my estimate still comes out more like 0.1% than like 5%.
A friend recently asked how strongly I believe that my deconversion from Christianity was not a mistake. Here's my response, and for those of you who are not Christians, I'm just wondering what numbers you would give:
"There is a part of me that wants to say the chance is far less than 1 percent. But when I consider what 1% must mean about my ability to follow complex arguments and base my judgement on the right premises, it seems absurd to say that.
Trying to honestly estimate the chance that I'm wrong about the Bible being generally reliable is a fascinating exercise... I know the number is low, but I'm not sure how low.
Today I would give myself a 1 in 20 chance of being wrong. If I were to consider the arguments of 20 other groups similar to Christian theologians, I would probably misunderstand them at least 1 time in 20. After talking with 20 groups that have a very different worldview, I might think they are all are mistaken, but once in a while, maybe 5% of the time, it would actually be me.
Wow, 5%!?! If I convert that into "There is a 5% probability that the God of the Bible exists and will send me to hell", I feel scared. But I know how to cheer myself up: I just say, "No way, the chance I'll end up in hell MUST be less than 5%. After all, the God of the Bible is CLEARLY just a big, mean alpha-monkey and... [rehearse all the atheistic arguments here]".
This back-and-forth from certainty to uncertainty makes me feel like I'm doing something seriously wrong.
So what about you? What chance do you place on some variant of Christianity turning up to be true, and what chance do you think a god of some sort exists?"
Numbers please.