When is a Religious Belief Delusional?

[Mister Agenda]

It is perfectly reasonable, and probably socially advantageous, to believe what your parents and apparently everyone in your close community believe. It is not a delusion to fail to construct the apparatus of critical thinking that would lead you to modify or abandon your belief system...and because it is a system, it's difficult to let go of parts without the whole thing collapsing. I was not deluded before I became an atheist, I was mistaken.

Religion is a social construct that persists because it has evolved to do so. Like any other institution with competition, there are winners and losers, and those that persist the longest have been the most successful at retaining members despite arguments and evidence that ought to whittle away at them. The first layer of defense in protecting your flock from effective persuasion is to convince them that it is virtuous to reject evidence and arguments against the faith, no matter what they are. To the person who is the target of all this, it can certainly feel like they are receiving all kinds of evidence and reasons for retaining their faith in the face of critiques from outsiders.

I think it is more fair and accurate in most cases to say believers have been successfully indoctrinated than that they are delusional. The guy who thinks squirrels are the Illuminati was not raised to believe that his whole formative years. That doesn't mean no religious beliefs are delusional, they can certainly rise to that level. But there's a clear difference between being indoctrinated and being deluded, mainly that you're not under tremendous social pressure to accept the idea that the squirrels are secretly running the world.

It's said (paraphrasing) that if one person thinks something crazy, it's a delusion, if a million people think something is crazy, it's a religion. There is a real difference in what's going on in those two cases.