Ad hocness and priors will differ from person to person and from time to time. Don't assume everybody is only rational to share your priors.— #RealAtheology (@Justinsweh) August 27, 2015
Normally this sort of sentiment would get my full endorsement. The idea seems pretty straight forward, once you've gotten to a certain level of philosophical understanding anyway. In the end I may be agreeing with Justin here, but I want to try and hash our my thoughts on the subject, and writing helps. Jump below the fold for my thoughts.
On reading this, it immediately sprung this idea of there being a problem that regular old "creationism" shares with its more ridiculous counterpart, Young Earth Creationism (YEC).
Basically, what makes someone like William Lane Craig and the other peddlers of Biola Bullshit, who think a god created the physical universe ~13 billion years ago, more reasonable or rational than Ken Ham who thinks a god created the physical universe ~6-10 thousand years ago?
At first glance it seems pretty simple: Craig follows the evidence and shares our assumptions. If we assume the laws of nature apply to matter and energy and we observe the evidence, we will apply general relativity to the evidence. Tracing things back we will eventually see the universe came from this hot dense state that was the beginning of space and time as we know it, and that process took ~13 billion years.
Ham, on the contrary, thinks the bible is literally true in all details, and he thinks it entails that the universe was only created in 6 literal days, roughly 10k years ago. In order to combat evidence to the contrary, Ham challenges the assumption science has that matter and energy behave the same way across time and space. Basically Ham denies that the laws of nature apply equally and everywhere. A good example is that the thinks the speed of light is not a constant, and that it has slowed down substantially post-creation, until it's settled on the speed it's on now, etc.
Problems with Ham
The biggest hurdle facing Ham is that he has no principled reason to think that the laws of nature have not applied consistently. He merely assumes it because otherwise the evidence would contradict the bible, which he also assumes to be literally true.
Whats worse is that if we do assume the laws of nature applied consistently then we are able to make a number of verifiable predictions, which we in turn have actually verified. In order to get around those problems, Ham keeps adding ad-hoc assumptions or rationalizations to get around the problems. This continues in perpetuity.
Problems with Creationism
Seemingly modern creationists like Craig don't have Ham's problems. They're just like the rest of us and assumes the laws of nature apply uniformly to matter and energy, right?
Well not quite.
These people will endorse the idea that matter/energy behave according to the laws of nature, but only up to a point. They may try to use the big bang as a justification to believe that the laws of nature couldn't always apply, but this betrays a superficial or dishonest understanding of what the big bang actually entails.
When it comes time to consider what things like quantum mechanics says about things like time and quantum fields always existing, these creationists start becoming a lot like Ken Ham. All of a sudden things like QM can't properly describe the ontology of reality. Or they start discussing how logically possible scenarios exist where god can create a universe that looks like it has always existed, but really is only finitely old.
A Relevant Difference?
Despite playing what looks like much the same game as their YEC brethren, I think there's a difference in the two approaches.
The modern creationists don't want to deny that the laws of nature stopped applying at some point, or that they've changed over time.
What they do want is to take different philosophical views on what fundamental things like time just have to be, and so interpret the meaning of what are formulated as "laws of nature" differently than what scientists do.
So it's a matter of differing "first philosophy", that is the assumptions we're forced to make before we can evaluate evidence.
But isn't this exactly what YEC's do? They hold a "first philosophy" that the bible is the inerrant word of god, and so they interpret the evidence in whatever light they have to in order to make it fit that paradigm.
What makes YEC Irrational?
So creationism and YEC both have a first philosophy they apply to the evidence, but then so does science and naturalism, at least nominally. This is because even if we approach the situation by saying "we will make a minimal set of assumptions as possible and base our metaphysics on what science says" is itself a "first philosophy" of sorts.
So just having a first philosophy isn't inherently what makes YEC irrational.
What makes YEC irrational is that it must continually make more and more ad hoc assumptions, while rejecting assumptions that make consistently verifiable predictions.
Modern creationism by contrast makes a set of assumptions, but those assumptions don't go against verifiable predictions. When modern creationist metaphysics contradicts what science generally accepts, it does so in ways that are inherently unfalsifiable.
That isn't enough to simply reject creationist metaphysics, since naturalism does much the same thing.
I suppose in the end I agree with Justin's original idea, though I think this line of thought could have some inherent problems for theism. That'll have to wait for another day though.