When I first read "Belief in Belief", I liked it, and agreed with it, but I thought it was describing a curiousity; an exotic specimen of irrationality for us to oooh and aaah over. I mentally applied it to Unitarians and Reform Jews and that was about it.
I've since started wondering more and more if it actually describes a majority of religious people. I don't know if this is how Eliezer intended it, but it was two things that really convinced me:
The first reason was behavior. Most theists I know occasionally deviate from their religious principles; not egregiously, but they're far from perfect. But when I imagine a world that would make me believe religion with certainty - a world where angels routinely descend to people's bedsides to carry their souls to Heaven, or where Satan allows National Geographic into Hell to film a documentary - I find it hard to imagine people sleeping in on Sundays. Not even the most hardened criminal will steal when the policeman's right in front of him and the punishment is infinite.
The second was a webcomic: http://www.heavingdeadcats.com/wp-content/uploads/2009/02/file1126-2.jpg It wasn't so much that theists wouldn't drink the poison as that they'd be surprised, even offended at being asked. It would seem like a cheap trick. Whereas (for example) I would be happy to prove my "faith" in science by ingesting poison after I'd taken an antidote proven to work in clinical trials.
I see two ways this issue is directly important to rationalists:
Is this solely a religious phenomenon, or are our own beliefs vulnerable to this kind of self-deception?
What kind of tests can we create to determine whether a belief is sincerely held?
And yet, Matthew 7:22-23
22 Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works?
23 And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.
Mere belief in belief is also, it would seem, not enough.
The problem, I think, is that most people are looking for the quick-fix, easy-button, where they don't have to actually do anything.
So when they see things like Matthew 17:20
And Jesus said unto them, Becaus...
I recently spoke with a person who... it's difficult to describe. Nominally, she was an Orthodox Jew. She was also highly intelligent, conversant with some of the archaeological evidence against her religion, and the shallow standard arguments against religion that religious people know about. For example, she knew that Mordecai, Esther, Haman, and Vashti were not in the Persian historical records, but that there was a corresponding old Persian legend about the Babylonian gods Marduk and Ishtar, and the rival Elamite gods Humman and Vashti. She knows this, and she still celebrates Purim. One of those highly intelligent religious people who stew in their own contradictions for years, elaborating and tweaking, until their minds look like the inside of an M. C. Escher painting.
Most people like this will pretend that they are much too wise to talk to atheists, but she was willing to talk with me for a few hours.
As a result, I now understand at least one more thing about self-deception that I didn't explicitly understand before—namely, that you don't have to really deceive yourself so long as you believe you've deceived yourself. Call it "belief in self-deception".
When this woman was in high school, she thought she was an atheist. But she decided, at that time, that she should act as if she believed in God. And then—she told me earnestly—over time, she came to really believe in God.
So far as I can tell, she is completely wrong about that. Always throughout our conversation, she said, over and over, "I believe in God", never once, "There is a God." When I asked her why she was religious, she never once talked about the consequences of God existing, only about the consequences of believing in God. Never, "God will help me", always, "my belief in God helps me". When I put to her, "Someone who just wanted the truth and looked at our universe would not even invent God as a hypothesis," she agreed outright.
She hasn't actually deceived herself into believing that God exists or that the Jewish religion is true. Not even close, so far as I can tell.
On the other hand, I think she really does believe she has deceived herself.
So although she does not receive any benefit of believing in God—because she doesn't—she honestly believes she has deceived herself into believing in God, and so she honestly expects to receive the benefits that she associates with deceiving oneself into believing in God; and that, I suppose, ought to produce much the same placebo effect as actually believing in God.
And this may explain why she was motivated to earnestly defend the statement that she believed in God from my skeptical questioning, while never saying "Oh, and by the way, God actually does exist" or even seeming the slightest bit interested in the proposition.