People usually think that because it looks like a cop-out; to outsiders, it looks like: I say 'this coin will turn out to be heads all the time', and when someone flips that coin and it turns out tails, I respond by saying 'well I was being figurative; not literally all the time'. When they keep flipping it, and it turns out tails half the time, and heads half, and I respond when it turns out tails by saying that 'I didn't mean that the result facing up would necessarily be heads; you have to turn it over onto the back of your hand, after all', but when it turns out heads I say 'I WAS RIGHT SEE', it reeks of dishonesty.
Which, really, is just people trying to clump all of Christianity into one group and saying that they all think the same way and should have their arguments be consistent with each other, and there were a few small conflicts concerning exactly that inconsistency sometime in the past...I think it was called the Thirty Years War or something?
Anyway. Usually my bigger question is what makes X right and not-X wrong. Rather than try to disprove the bible, as I have no vested interest in whether or not someone else is religious until they use that religion as an excuse/believe it tells them to do things that will hurt other people, I ask people to prove it to me. Why should I believe a book that's been translated and misinterpreted and copied over and over and over again? How many errors were made in that process? How many of them were never caught? I don't even know Hebrew, or Latin, so I can't even try and posit interesting misspellings of words that might have ended up commonplace.