When I look at people from $largeMainstreamReligion, I see people who will defend it as "the genesis of human life and the only source of truth" as a fact of the community you're supposed to accept. But then looking at their lives, they pay at best a lip service to the actual contents of that "source of truth", and instead only participate in the accepted traditions.
Basically, I feel that religions, fandoms, school associations ("I'm a Harvard Alumni"), etc. all work pretty much in the very same way.
What's more relevant is the differences. Funclubs' purpose is fun, I presume. Programming is serving humanity, I have no doubt. Political parties are in a way like football, a gentlemen game played by thieves. Companies are far from meaninglessness, they serve clear organizational and legal and taxes etc purposes.
Religions (edit: I'm familiar with) are built on deception to control people, they are not like fanclubs, programming, companies.
It looks like a viral infection, yes, that's how it spreads: an evil payload wrapped in good ideas. It's a tool to control people even if it's not used everywhere all the time, even if sometimes it's used for good. And finally, yes, the believers have no intention to deceive; they are the ones deceived and since most of them are essentially good people they naturally want to spread the "truth" by telling others about it.
Thinking about it, the fandom that I'm part of shows quite some resemblance to a religious organization.
Doesn't matter. What other commenters here try to point out as well, a lot - if not most - organizations are built around one fiction or another. Some examples:
- Fanclubs, fandoms, convent attendees - those are literally communities built around fairy tales.
- Programming language communities - built around ever-changing artifacts of human imagination, they too have to deal with possible change of direction impacting attendance.
- Political parties - organized around some people's understanding of some ideas, + shitton of meaningless slogans that everyone interprets how they like. Exist mostly to self-perpetuate, as evidenced whenever any established party has anything meaningful to say or do; suddenly the official program takes second place towards what helps electability.
- Companies - the ultimate bubbles of meaninglessness, they in principle - and often in practice - exist as an ever charging group of people bound together by will to make money on ever changing product for ever changing market, lead by ever changing board.
I'd add nationalities, as there's plenty of crazy fiction going on in there, but they're at least usually bound geographically, so there's that.
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The point being, many if not most organizations are built around some fairy tale or other, and what an organization is built around rarely matters to anything. What matters is how strong the community is, and that's pretty much purely social factor, without any actual dependence on objective reality.