Your strength as a rationalist is your ability to be more confused by fiction than by reality.

Yet, when a person of even moderate cleverness wishes to deceive you, this "strength" can be turned against you. Context is everything.

As Donald DeMarco asks in "Are Your Lights On?", WHO is it that is bringing me this problem?

...what if we all have some form of brain damage in common, so that none of us notice some simple and obvious fact?

Aren't things "obvious" by virtue of being noticed (or noticeABLE) by nearly everyone? Not trying to be difficult, but just trying to wrap my head around the idea that we could, all of us, be suffering such a severe cognitive malfunction. (I am thinking, here, of the liar's paradox.) And trying to wrap my head around the idea that now we could sit here in front of our computers and say anything worthwhile about it.

But for the sake of playing the game: "There are no coincidences."

I've heard of several. I don't know stats on what proportion of Bible scholars de-convert.

Bart D. Ehrman - author of a book saying lots of the New Testament was forged

Francesca Stavrakopoulou (unclear when she became atheist)

Robert Price - went from Baptist minister to Cthulu mythologist. Not kidding.

Jacques Berlinerblau, who does say he knows few openly atheist biblical scholars.

There were quite a few troublemaking preachers who fell afoul of the law in Judaea at the time, many of whom were called Jesus - it was a very common name at the time.

However, one of the big problems with assuming one of these fellows (or another we have no documentation of) was the human seed for Christianity is the early Christian tradition of docetism - that Christ had no corporeal existence at all, and was just an idea. Paul of Tarsus certainly seems to think along these lines, despite the later caution against said notion in John.

This also helps explain the curious lack of non-Biblical evidence for such a person, in histories where one would expect it.

It is often noted by apologists that scholars think there's enough evidence to say there was a human seed for Christianity. However, "scholar" in this context is a weasel word - most are Christians and theologians, who would have tremendous trouble (personal and professional) coming to the opposite conclusion at all. The epistemological standards accepted in Biblical history in particular are generally bloody awful and an embarrassment to other ancient historians.

For a pile of stuff on this issue I recommend the RationalWiki article, which I have worked extensively on. (One of the other main contributors just so happens to be an atheist who was a student of Biblical history.)

(I find this stuff fascinating, if only for the psychopathology. And, as such strident atheists as Mencken, Dawkins and Hitchens have noted, you can't be highly literate in English without knowing the KJV, much as you need to know Shakespeare and Greek mythology. The trouble is that ... well, it's like you wanted to study the Odyssey or the Iliad but the only people to learn from were people who (a) actually believed in all the gods named therein (b) really wanted you to as well.)

Welcome!

If by "rationalist", the LW community means someone who believes it is possible and desirable to make at least the most important judgements solely by the use of reason operating on empirically demonstrable facts

You'll be relieved to know that's not quite the Less Wrong dogma; if you observe that your conscious deliberations make worse decisions in a certain sphere than your instincts, then (at least until you find a better conscious deliberation) you should rely on your instincts in that domain.

LWers are generally optimistic about applying conscious deliberation/empirical evidence/mathematical models in most cases besides immediate social decisions, though.

All the kinds of knowledge you describe are subclasses of rational knowledge. Is there irrational knowledge?

This is, in practice, a form of equivocation between epsilon uncertainty and sufficient uncertainty to take seriously as an argument.

1. There is technically no such thing as certainty.
2. Therefore, the uncertainty in [argument I don't like] is non-negligible.

Step 2 is the tricky one. I suggest reviewing But There's Still A Chance, Right? Humans are, in general, really bad at feeling the difference between epsilon uncertainty and sufficient uncertainty to be worth taking notice of.

Although I am Catholic, I acknowledge that by certain standards of proof, the existence of the Jesus as described in the Gospels is uncertain.

Those pesky standards that don't consist of "faith". ;)

Documentary evidence that dates from the time of Jesus' supposed life and death, which describes a religious leader called Jesus who started a splinter sect of Judaism would do it.

What documentary evidence for any other religious leaders that started other splinter sects of Judaism at the time do you have?

If you don't have any direct evidence for any specific one of those leaders, does that mean there didn't exist any such splinter sects at the time?

The preponderance of the evidence would seem to be that he really did exist.

Bible scholars have a consensus that this is the case, although whether they are doing any actual scholarship with regard to the issue is questionable. Atheists by and large do not become Bible scholars, and the mind-killing effects of religion mean that theists tend to do notably poor scholarship in this particular area.

However when a rationalist tries to drill down to the actual evidence you find that nothing is there, apart from Bible scholars reading the Bible and saying "this Paul guy seems legit, I don't think he'd have made that up".