I've heard in a number of debates, especially on the historicity of the Resurrection (like the very interesting 6-parter between Robert M Price and Don Johnson), that the reason a skeptic doesn't believe the Resurrection of Jesus is that they have a presupposition against miracles, or the supernatural, and simply discount it on principle. There are two mistakes with this idea, which I find illustrative of ignorance of proper scientific thinking.
- Most of these biases against miracles are learned from evidence, as most miracle claims come up empty. So it is not an irrational bias, but a rational one, based on life experience.
- It shouldn't matter anyway - if something is true, then one should be able to convince even a skeptic. And it is perfectly natural to distrust extraordinary claims, and it is the job of the claimant to make the case.
I thought of two examples from my life where I was skeptical of an extraordinary claim, one where it turned out my perspective was correct and the other not.
- In the 1990's, the first evidence for the acclerating universe came out. I remember thinking, "No way this is true." At the time, I thought their calibration of the supernovae used as standard candles was somehow incorrect. Did the researchers approach this skepticism with "oh, you just are biased against theories that propose unknown external forces, or violations of known laws"? No. Other groups repeated it, they confirmed any calibration, and came up with a theoretical structure (using the Cosmological Constant) to describe it. Then I was convinced. Was I wrong in my skepticism? Absolutely not. The response to skeptics is to bring the evidence to bear on it. If the evidence is not enough to convince a reasonable skeptic, then we can't be particularly confident in it.
- Recently, there was some data indicating possibly faster-than-light neutrinos. I had a response to this here, where I was skeptical of the result. Again, it was a group of careful scientists who had done the measurments, and had taken into account everything they could think of. I still didn't believe it. Did the researchers approach this skepticism with "oh, you just are biased against theories that propose unknown external forces, or violations of known laws"? No. Others tried to analyze the same data and the set up, and the scientists explored other explanations. [Turned out to be a loose cable]. Here again, my skepticism was well placed.
It's not bias to be skeptical. It isn't irrational to demand a higher-than-average standard for extraordinary claims, no matter what. If you make such a claim, and that higher-than-average standard is not met, then you cannot be confident in that claim. It doesn't matter whether the claim is religious or scientific, the same rules apply.