Why aren't creationism and natural science on the same intellectual level?

In the infamous creation museum a strategically very shrewd exhibit, where a scientist and a biblical scholar both study the same fossils, is being presented: The sign says “different scientists can reach very different conclusions, depending on their starting assumptions.” The argument obviously is that both interpretations are on the same intellectual level and are therefore equally valid. Why is this wrong? My gut feeling is that you use far more assumptions when starting from the position that the Bible is true (but is having more assumptions problematic in itself?), you are running into all kinds of problems when you state that "anything goes" (Stephen Law calls this "going nuclear") - effectively it states that no real knowledge whatsoever is possible. I think key in this debate is the demarcation problem but my question is more practical: What is the best rebuttal against (the philosophical mindset of) this exhibit?