>” I find this to be an extraordinarily irrational position.”
Well, I’m not advocating for it, I’m merely noting its existence. I have been related to and worked with (e.g.) religious people of the type referred to as “fundamentalist,” and it was my understanding of their worldview that they did not grant that other religious beliefs were “equally valid.” I think we see at the moment how this is also (not) playing out in Middle Eastern politics. You’re not going to convince me that anyone can convince ISIS that other religious viewpoints are “equally valid.” I posit that people of fundamental belief systems — religious, sure, but others as well — don’t really accept that all other viewpoints are equally valid.
“Why in the world would anyone think that something they believe must be true merely because they believe it?” That’s a good question for those who have such beliefs. I do wonder whether in your hierarchy of belief systems you’ll grant that your viewpoints regarding science are just as likely to be right or wrong as, say, young-earth creationism, and that you would, for example, extend your all-belief-systems-are-valid disposition to encouraging school systems to include all belief systems in, for example, science curricula.