All beliefs are probabilistic and can change. The evidence that would convince us that Christianity is true would have to be commensurate with the prior telling us today that it is false. The existence of that low prior is the proof that it's very likely false (factoring in our uncertainty about some things).

(By the word 'prove', I obviously didn't mean a logical proof that sets the probability to zero; just one that makes the probability so low that theory would never rise to the level of conscious consideration.)

Why do I think our prior for Christianity should be very low?

First, because it makes supernatural claims; that is, claims which are by definition counter to all previous observations which we had used to determine the natural laws.

Second, because its core claims (and future predictions) are similar to many sets of (mutually contradictory) claims made by many other religions, which implies that generating such claims and eyewitness testimony (as opposed to lasting miraculous artifacts or states of nature) is a natural human behavior which doesn't need further explanation.

Third, because we know that Christianity and its dogmas have changed a lot during its history, and many sects have risen and fallen which have violently disagreed over every possible point of theology. Even if we assign a high probability to some variant of Christianity being true and ignore all other world religions (actual and possible), the average probability of any specific branch of Christianity would still be low, although not nearly as astronomically low as due to the other reasons given. And since we can trace clear human causes for the beliefs of many sects - like Luther postulating that since Catholic clergy was corrupt, their theology must also be wrong, or like many sects that were declared heretical for political reasons - it's likely that all sects' beliefs had human causes, and evolved in large part from previous, non-Christian beliefs.

Fourth, and generalizing the previous point, the reason we're even talking about Christianity isn't its claims. It's not because some Christian prophecies or supernatural beliefs unexpectedly came true. Rather, it's because many people are Christians and we grew up in or near Christian culture. But a great many religions that once flourished are now diminished or lost to history. And even Christians themselves (unlike some other religions) don't usually argue that the spread of their religion is a sign that it must be right; on the contrary, they venerate those who believed when Christians were few and persecuted.

Agnostics

It's true that a lot of people call themselves agnostics, which seems to indicate (1) not being completely convinced by any argument against theism while also (2) not having a commitment to any particular religion. However, I think the great majority of people who call themselves agnostics fall into one of these categories:

• People who prefer to avoid too-committal terms like "atheist", either because there's a stigma attached to overt atheism where they are or because they think "atheist" implies absolute certainty.
• People who haven't really thought the matter through very much.
• People who are agnostic about the existence of some sort of deity but strongly convinced that e.g. there is almost certainly no supremely good and powerful being who takes a personal interest in human affairs.

I would expect people in the first and third groups to share my opinion about arguments from evil, though the third lot would rightly observe that e.g. such arguments tell us nothing about superbeings who just don't care about our affairs.

People in the second group might well not be very convinced by arguments from evil, but I would expect that if they gave serious consideration to such arguments they would typically see them as very strong.

"Everyone thinks there is a convincing argument"

That's not quite what I'm saying. I'm saying that there are, in fact, arguments that I would expect to be very convincing if looked at seriously by a sizable majority of people not committed to the religions in question. Of course those who haven't seriously considered such arguments will not yet be convinced.

Your own epistemic situation

I find it very interesting that you aren't very convinced by arguments from evil despite having rejected Christianity, but I don't think there's anything further I can say without having any idea why it is that you aren't convinced. You say it's because there's a particular answer you find reasonable, but I've no idea what that answer is :-).

You do mention Scott's "Answer to Job", which is very ingenious. It's a good answer to arguments-from-evil that end "and therefore it is absolutely impossible that there is a benevolent god", but I would consider such arguments overreaching even without that particular answer. Is it any good as an answer to "evidential" arguments that take the quantity and distribution of Bad Stuff in our world merely as evidence? Well, I guess that depends on (1) how likely Scott's scenario is a priori and (2) how credible it is that our world is, so to speak, a random pick from all possible worlds where good outweighs bad, weighted by number of intelligent agents or something of the kind. To #1, I say: not terribly likely, because I am not convinced that good outweighs bad in our world. (Which is not at all the same thing as saying that many people in our world would rather die than live.) To #2, I say: not credible at all; I would expect a random observer from a multiverse containing all possible more-good-than-bad worlds to see something very very very different from what I see. (I suspect the great majority of observers in such worlds are something like Boltzmann brains.)

"Atheistic convictions are often the result of non-evidential commitments"

Oh, absolutely. I wasn't meaning to make any comment on the relative merits of theists and atheists. I was just addressing an obvious argument against any claim that there's good evidence against theism, namely that lots of apparently sensible people are theists. (I firmly agree that you likewise can't reject the claim that there's good evidence against atheism just because lots of apparently sensible people are atheists.)

(Highly intelligent converts like Leah Libresco and Ed Feser would be evidence against any claim that the only reason for not being convinced by atheistic arguments is prior religious commitment. But I have not been making that claim, at least not deliberately.)