Fair enough up to a point.
But as far as the dayglo interplanetary mammoth is concerned. I was trying to point out that the weakness of the scenario apart from rhetorical purposes, is that the mammoth doesn't have any explanatory value.
My fifth-dimensional aliens do have some explanatory value, they purport to explain the mysterious arrival of the remarkable molecule DNA, so they're not exactly parallel cases.
I'm well aware that the 5d aliens leave plenty if not more to be explained. But they don't do nothing. And as it happens lots of people do believe that or something like that, and precisely because it coheres with their experience and worldview better than the "scientific" account.
But the reason I put the point was not to argue the relative merits of dawkinian fundamentalism over alien experimentation as explanations of life, but because I wanted to point out that people do believe the most unlikely things, without evidence, when their theory is not falsifiable, and is based only on coherence with the rest of their worldview, and they have no evidence for it, it just must be so. And yet, falsifiability is supposed by many to be a criterion for a scientific theory.
( at least when you're investigating physical reality it's a reasonable assumption that it won't deliberately deceive you, which isn't such a good assumption when investigating the human world.)
But it's a poor situation we're in when you can't have any theory at all about events for which you can't get direct empirical evidence. What are we supposed to do, just say that wherever we can't get empirical evidence, there is no truth... ? That leads straight to solipsism.
The fact is that most of what we call knowledge is based on hearsay from sources we consider reliable, and on inference. It also seems to me that we decide which sources we consider reliable intuitively by seeing how well they cohere with the rest of our worldview.
From a philosophical point of view, as far as I can see, this means that when you're discussing competing worldviews, "not credible" has little more meaning than -I can't believe it-" so it's not much of an argument. It's actually an objectification of a feeling.
Did you know this, there was an astronomer, a scientist, who checked out Galileo's observations and finding them to be correct, concluded that while telescopes tell the truth about terrestrial bodies, they are inaccurate about celestial bodies. Just shows, almost any evidence can be tainted when the worldview it conflicts with is sufficiently entrenched.
But on the other hand, there is such a thing as incredible. The dayglo interplanetary mammoth is incredible. I know you don't believe it. you know etc. So we draw the line somewhere. I haven't figured this out entirely. But at the moment it seems to me that contrary to what you said in your post, you can't choose any beliefs you fancy.. Your beliefs aren't subject to choice. But in another sense you do choose your beliefs, by deciding what kind of sources you consider reliable, and what kind of worldview you have which in a way is like choosing what tribe you want to be part of..