Bias: Acceptable, and inescapable

The fact is, no creature capable of independent thought is without bias. If you have an opinion, great or small, about any topic, you have a bias. Even when you first approach any given topic, your presuppositions about that topic will determine how you form opinions about it.

According to Dictionary.com, bias is "a particular tendency, trend, inclination, feeling, or opinion, especially (but not exclusively) one that is preconceived or unreasoned". (Brackets mine). I have a particular opinion regarding Christianity. So do you. Whether a fellow believer or a hardened unbeliever, you have a particular opinion regarding Christianity. But what's more here is that I actually admit I am biased. But if you're so biased against Christianity that you can rule out any evidence for Christianity based solely on the fact that it comes from a Christian source, you're not just biased, but unreasonably biased. Let's demonstrate this with a few hypothetical debates:

Round earther: photos of the Earth show that it is round.

Flat earther: you would say that, you're biased!

Pro-vaxer: There's no evidence that vaccines cause autism, but even if they did, I'd rather have my child be autistic than catch polio.

Anti-vaxer: you would say that, you're biased!

Atheist: Evolution is proven by homology.

Non-Evolutionist: you would say that, you're biased!

You see, then, that bias does not necessarily mean wrong. You can actually be biased in favr of the right answer. Not only that, but even if a person is biased towards the wrong answer, like Evolution, "you're biased" is quite obviously not a valid response, and if you use it in your discussions, you suck at arguing.