SF, you're absolutely correct, everyone has biases, but I don't think all biases are equal. There are many evolution-believing scientists who are Christian (even most of them?), so I don't view this as a religious arguement as much as a scientific one. In any case, "evolution" arguements don't start from the conclusion that evolution is true. Creation arguements do, however.
The case for evolution is made by fossils, genetic mutation, DNA evidence, and observable evolution and speciation in the lab. In other words, tons of physical, testable, observable evidence. And also, more importantly, evolution isn't tied to any doctrine; if scientists find it's not true, then science is STRENGTHENED, not weakened. However, if creation is found to be untrue, then some people's religious doctrines have to be modified, and therefore there is a considerable psychological hurdle to overcome.
But your point is correct, everyone has biases, myself included. We should endeavor to minimize them, however, whereas I see folk like "Answers in Genesis" almost celebrating their biases.