Lukeprog, over at the blog "Commonsense Atheism" has written a blog post about assessing whether or not a religion or worldview is true. One of his criteria is 'Consistency with known facts'. He writes:
If a religious claim contradicts what is known in another field, this may be grounds for rejecting the religious claim, unless the religious claim is better supported than the other knowledge. For example, if a religious system claims that the earth was created 6,000 years ago, but millions of pieces of solid evidence from multiple fields of consistent research conclusively show the earth to be much older than that, then this gives us cause to reject the religious claim. If the religious claim is central to the religion, then the whole religion may be rejected.
I would extend this principle even further: Don't fall into the trap of accepting numerous gross, unsupported speculations and just-so stories that attempt to make reality fit the religion in question. Too many times I have seen Christians defend Biblical inerrancy with just-so stories and speculations to get around the apparent (and probably actual) contradictions in the Bible. But guess what? There's no reason to accept those just-so stories unless you are already committed to Bible inerrancy. So that makes their speculations circular, if one is trying to approach religion objectively, as one should. Let me give you another example: Mormons claim that the Native Americans are descended from Hebrews. But archaeology and DNA evidence conclusively shows that they are not. So what do the Mormons say to this? They say DNA is a young science and so it doesn't have all the answers yet. As for archaeology, absence of evidence is not evidence of absence. But again, realize that there is no reason to accept these ways of bullshitting around the facts unless you are already committed to defending Mormonism. But you should not be committed to Mormonism unless the facts bear it out as true. And if a Mormon accepts that, then they have to realize they are making a circular argument if they say that they are committed to Mormonism because the facts bear it out but then rely on their committment to Mormonism when the facts don't bear it out.
I would also add something else to Luke's post: It is possible that many religions are consistent with known facts, are logically consistent and consistent overall. So what one wants to look for is the religion or worldview that is the best overall explanation. The best overall explanation can be determined by explanatory scope, explanatory power, simplicity, and so on.