It's clear that questions about religious texts cause friction. So should we ban questions that are specifically about religious texts? If so, how wide should the ban be: only about the Bible (which is what generates the most contention), or more general? Note that we must not overreach — we're not going to ban Star Wars even if some people declare their religion as Jedi.
Here's the question you should be asking yourself: Would a reasonable person walking into a bookstore expect to see a copy of the Bible, Koran or other widely-recognized religious text in the Science Fiction and Fantasy section, unless somebody put it there to make a statement?
Let me offer a concrete example.
The Last Question is a sweeping short story by Isaac Asimov, about the universe running down due to entropy. Without giving too much of the story away, the last question is "Can entropy be reversed?" It is a question posed to a massive supercomputer, which spends centuries trying to solve it.
I think it's reasonable to say that this short story has significant religious undertones. Now, if it were possible for me to write a constructive question that asks how this story relates to Christian theology, I would say that the question would be on-topic, because the primary subject is an unambiguously SFF short story.
If, on the other hand, I managed to write a constructive question that asks how Genesis 1:3 of the Old Testament is illuminated by this story, I would have to say that such a question would be squarely off-topic, because the principal subject of the question deals with a work that is not SFF, but rather uses an SFF story periperally to make a point about religion.
For all those questions that are various shades of gray between these two examples, the mods for SFF should ask: Does this question make the site a better Science Fiction and Fantasy site? Does it adequately and constructively serve the mission of the SFF participants?
I think that a ban on questions on religious works is appropriate. It leaves us open to too much controversial debate, potentially offended visitors, and the likelihood of duplicated content with other SE sites (i.e. the ones dedicated towards those specific religions).
As for how we define the scope of religious topics, I think it is fair to use the organization of typical franchise brick-and-mortar book stores. If it would be reasonable to expect that a book on the topic at hand would likely be found in the religion section (e.g. relating to Christianity, Judaism, Islam, Taoism, Wicca, etc.) then it is off-topic. Books typically put into mythology, history, etc. would likely be considered "non-religious".
To be safe, I believe that anything likely to be found under the "New Age" section should also be treated as religion.
One major disclaimer: if any question that would fall under the religious description above can be tied directly to a specific work of fiction, then it is acceptable.
Example 2: Even though many books on reincarnation can be found in the New Age section, and it is a component of several major religions, questions about whether Baron Harkonnen was actually spiritually reincarnated in Alia in the Dune saga would be entirely on topic.
Example 3: His Dark Materials trilogy which has strong religious undertones, and is religiously controversial, is on topic as it is first and foremost a work of fiction.
Example 4: questions tying C. S. Lewis's character Aslan with Christian themes of sacrifice, martyrdom, and ressurrection are on topic.
Sorry for putting in a 2nd answer, but this is quite different than any others here. Something was bothering me about the question that kicked this off and about our discussion, and I finally realized what it was that bothers me and how to explain what I think the limits should be here.
For reference, the question that started the discussion was, "How did Noah fit all the animals in the Ark?"
This question makes the assumption that a story that's part of the core of a particular religion is fiction (either SF or F). While the majority (last I looked at demographics) do not take the Bible literally, it is well known that there ar also many people who do take it literally. While it may be asked without malice, I have known non-believers who will bring up questions like this in conversation out of malice or arrogance.
I know of people who have done that kind of thing because they think if they point out inconsistencies in someone's faith, they'll just suddenly drop their beliefs. I've known others who do it just to taunt and be mean, and others who are so arrogantly proud of having no need to believe (as they might put it) that they need to intentionally ask such questions as a way of saying, "Your beliefs are stupid."
And, once in a great while, and mean a very great while, I hear someone ask a question like that of a believer for the purpose of honest and open discussion and an attempt to understand another person and their faith.
But, in my life, I've seen questions like that asked more out of malice or arrogance than out of open curiosity. I'd dare to say 99% of the time such questions are more from a negative intent than a positive one.
On the other hand, asking about Titans and why they weren't as powerful as the Greek Gods deals with what, to some, is a religion (as someone pointed out to me). But it's not posed in a way that it is disrespectful of the religion involved with the question and with possible answers.
So it comes back down to respect for other religions and points already made.
I think an easy litmus test for questions on religion would be to ask, "Does this question/answer/post imply that a religion or a notable part of a religion is either false, malicious, or misleading?"
I think this question will eliminate the vast majority of disrespectful questions about religion. It provides a clear and objective line and rule to follow. The ones that are left that are disrespectful or offensive will likely be covered by normal rules and expectations about courtesy.
In other words, religious questions are not necessarily off topic, but ones that lead to a "Yes" answer to the above question are disallowed.
My vote for DVK's #2 but with a small adjustment:
Don't limit this exclusion to religions, but to particular books.
E.g. a question about Jewish religion in Dune books is on topic because Dune is clearly a work of fiction, even though it involves a religious group which exists in real life. On the other hand, questions about something described in a religious book are off topic not because they are about religion but because the book is a religious one.
The example with newly emerging Jedi religion is actually a very good one for making that comparison. Questions about the Jedi in Star Wars universe are obviously on topic. Now, imagine that our real world followers of Jediism actually write their religious book with sermons and all that. Questions about topics and events in that hypothetical book should be off topic. That is, assuming that George Lucas doesn't sue them out of existence first.
EDIT: My position on the matter is focused almost exclusively to the aspect of a question being on or off topic. As for respecting other peoples beliefs and not offending them, I think that this should apply to any post on SE regardless of whether it is about religion or gardening. Not actively trying to insult someone is in the FAQ of every SE site, specifically Be nice. That said, when it comes to religion people tend to be a bit more touchy and that probably requires an extra level of tactfulness when dealing with such questions. But the attitude of not being a jerk should definitely not be limited to dealing with religion related topics.
I see 3 possibilities:
Limit it to whichever religion would have its own on-topic theological site. A wee bit unfair as there's only 2 or 3 now (I know of Christianity, Judaism, and I'm pretty sure Islam is sitting someplace on Area51).
Limit it to religions that didn't clearly start out from a fiction story. E.g. Chthulu/Jedi/Anything based in Alistair Crawly (sp?), we know for a fact it is based on a work created as fiction. Precise inclusion/exclusion rules should probably be decided by explicit META.scifi.SE voting.
Go all nuanced. E.g. questions that are about Judaism, must be asked in a respectful way (sorry, "magic" tag means the question gets wacked); and be a GOOD question related to religious text treated as creative work. E.g. comparing archetypes in Old Testament with Cryptonomicon's archetype theory.
If we do this:
Any question like that must have a "RELIGION-MAY-OFFEND" tag
Any question with that tag requires a separate vote on META.
Any nasty comment arguments are aggressively wiped by moderators (as in, erring on the side of over-wiping).
The policy must have periodic reviews, and if we find that >66% of such questions are of low collective value to the site within couple of months, we revisit the rules and go for more blanket type of ban.
I can support questions regarding religious texts as being off-topic for purely pragmatic reasons, but not for logical ones.
People can be extremely sensitive regarding their religion, and we're all trying to be nice here. If people could simply respect each other's beliefs and not get offended, then it would be fine, but far too few people can.
I don't want anyone to emotionally implode and rage quit the site because the site recognizes the reality that not everyone believes in their religion by allowing individuals to ask questions in line with their beliefs.
In other words, we're more likely to horribly offend someone by allowing these questions than by not allowing them, even though that's a little offensive as well.
No religion has a majority share of the world's population. For any religion, the people that believe in it literally are a minority.
Therefore, for every religious text, the majority of the world's population considers it a work of fiction.
Furthermore, given that these works include things that appear impossible given our current science, i.e. miracles, they would clearly fall in the realm of science fiction or fantasy.
So, if it weren't for the sensitivity issue, these would be on-topic.