Honestly, it really does come down to final authorities. The creationist position ultimately boils down to this: the Bible is the word of God, and all evidence must be interpreted in light of scripture. In this respect, the origins debate becomes a war of world-views.
But isn't that anti-scientific in the sense that it poisons the well? Going into something with a massive baseless assumption already taken for granted doesn't seem wise.
Even atheists begin with assumptions. The question isn't whether the axioms someone has in their worldview conflict with yours, it's whether they make logical sense when combined with the physical evidence. Young earth creationists have to go thru an extensive amount of assumptions, and they don't bother to explain why the very hyperactive God required to cram what the standard scientific geology and cosmology says takes millions and billions of years into just a few thousand has become so quiescent, but they do have a theory that makes internal sense, despite requiring a lot more complexity than the standard scientific model of how the universe works.
