At what point does faith become insanity?

[Belacqua]

No, it looks like I got the wrong end of the stick there, my mistake; I didn't know there was a specific group called "True Believers", I just thought he was talking generally as in 'I was a true/strong believer once', and just recounting my experiences of the same.

Oops, sorry, I think I was misleading there. I don't think there's a group called "True Believers," though of course they all think they're true believers. I assumed you meant you were just enthusiastic about your beliefs -- so no issue there. 

In my case I don't think I was 'insane' during that period, just delusional. A delusion to me just means a set of beliefs, stubbornly held, and largely resistent to reason/outside influence, primarily through massive amounts of confirmation bias. The same thing can happen in a mafia game, but I wouldn't (necessarily) call it insane.

I think this is the point I want to emphasize. Being really really wrong is not the same as being insane. Anybody who's raised that way, who has heard it from birth, is reasonable to believe it -- whether they're reasonable to KEEP believing it or not is of course a different issue. 

In my school, in Britain, theists were a minority. I don't remember any of my friends or classmates being theists, so I was the odd one out in that regard. So from my classmates perspectives, I guess I arguably could've appeared pretty insane, but from a different relative baseline, that of a Britain where my parents beliefs were/are pretty common/standard, if technically in the minority, less so. I can't really speak for America, never having lived there, with religion being so ubiquitous in one way or another, such that the only way to get anything done or be heard seems to be to join or start a religion/church. That's a very different baseline for comparison.

I've heard that Britain is overall less religious than the US. And of course the US history with Christianity is more Puritan and evangelical from the beginning, probably. In England there are socialist Christians and apparently less of the Jesus + Capitalism + guns = freedom sort of unpleasantness. 

I'm so old that when I was growing up religion was less of an issue in my American hometown. Probably 99% identified as Christian but the Moral Majority and others hadn't yet weaponized it politically. It was still considered impolite to talk religion or politics. My dad was a left-wing atheist and also City Manager for decades, but I suspect things have changed so much that he wouldn't be welcome in the government any more.