Irrational, yes, but not fundamentally so. Without supernatural beliefs, they’d have to at least think that they care about empirical reality. Their beliefs would be falsifiable, whether they’re willing to acknowledge it or not. [...]

That fundamental inability to be reasoned with, which I would consider fundamentally irrationality, is unique to supernatural beliefs.

i just do not think this at all nor do i think falsifiability is a meaningful consideration in this conversation (because people do not care about falsifiability, i'm sorry. to my knowledge this is well studied and the bulk of those studies show that proving someone wrong seldom influences their opinions in any meaningful way). you don't even have to get harmful here: just try reasoning with a person who thinks Pluto should still be a planet at this point about why it isn't. there is no rational underlying justification to continue to believe this, yet people will go so far as to say the Whole of Science got it wrong and there is no argument you can make to convince them. people will gladly die on fundamentally irrational hills and fundamentally be incapable of being talked out of defending those hills with or without religion. this is not a supernatural thing.