If you take the outside view, and account for the fact that sixty-something percent of people don’t believe in Christianity, it seems like (assuming you just learned that fact) you should update (a bit) towards Christianity not being true.

If you did know the percentages already, they should be already integrated in your priors, together with everything else you know about the subject.

Note that the majority of numbers are not prime. But if you write a computer program (assuming you’re quite good at it) and it tells you 11 is prime, you should probably assign a high probability to it being prime, even though the program might have a bug.