“ Such ridicule typically will not occur after a religious conversion brings a previous non-conformist into the fold of the culture’s dominant religion.”
"None of you think the major religions teach some insane things? Okay then."
I was on the phone so couldn't type much, but my point is the concept of the collective cognitive imperative (much better explained in the book than in Wikipedia, to be fair) would answer your question by saying "it's not that nobody thinks that: it's that enough people accept those insane things to the point that 1) they don't think they're insane things, 2) you'd be an outsider (or even considered insane) if you point out the fact that they're insane things.
I'll try to give an example that would work in my cultural context (South America): someone making a rain dance during a drought would be considered by most to be something from harmlessly silly to crazy. Someone praying to the christian god for guidance or help would be seen as normal.
I was trying to understand what you meant by “insane”, but you already moved the goalposts to “implausible”, so it’s not clear to me that you even know what you’re claiming.
However, if I were to take a guess, it’s something like “people sometimes believe things without proof”. But obviously this is not true only of religious people, other people have their own creation stories – the sole difference is their’s don’t involve worship. And I agree they can’t all be right, but perhaps one of them is.
I didn't move the goal posts; I just used a slightly different word. No offense, but it's ridiculous (sorry, "insane") that I'm dealing with pushback on the point the point that religious believe things that would be considered insane if not labeled as "religion". "There's an all-powerful being that is behind everything... etc." If you're not willing to give any ground on that, then it's not a productive discussion in the first place.
What about the non-religious claim: “There’s not an all-powerful being that is behind everything”? Just as “indefensible”, just as “implausible”, just as “insane”. The sole difference is that it doesn’t involve worship, and therefore categorically isn’t “religious”.
These are axioms, you cannot derive them, you can only derive from them. Saying “my axioms are rational, yours are ‘insane’!” is frankly childish, and speaks to a deep lack of understanding of the essence of reason.