The bias of unbelievers really shows when it comes to their attitude to the Bible. Any reference to the Bible, in any argument, is automatically seen as invalid simply because it refers to the Bible. Take, for example, the resurrection of Jesus. The Bible is the primary source for this claim. Without exception, all other sources were written later, meaning although they can be helpful, they are not half as strong as a first century source.
Even if you ignore its divine origins, the Bible is a historical source just like any other. There is no reason to discard it, or to treat it any differently from any other historical source. Even the argument that it is biased does not change a thing. After all, if a historical event happened, any eyewitness that recorded such an event is going to be biased towards the idea that it happened. Bias can go in the other direction too. If someone said the resurrection didn't happen, that would be a biased source against the resurrection, but no unbeliever would say such a source could be discounted simply because of its bias.
The desire to leave the Bible out of a discussion on Biblical events is not a valid one, but it does reveal something else. The only reason to leave the Bible out of such discussions is if you are biased against it. If your opinion on a subject can only be changed by those who do not wish to change it, you're not only biased, you are irrational. Of course someone who didn't believe in the resurrection is going to claim it didn't happen. Of course someone who believes the resurrection happened is going to claim it happened. If you write something you don't believe, you're not just unreliable, you're dishonest! Attempting to discount the Bible as a reliable historical source just because it is the Bible is just as circular as attempting to claim it's true just because it says it is.