It is a story I call "Fandom is a Pot-Luck Dinner," told for the benefit of people who might wonder about why Worldcon doesn't generally give free memberships to their volunteers/staff/committee/program participants in advance.
Imagine a group of six friends who are all foodies. They come up with the idea of having a series of pot-luck dinners where each person brings a dish and everyone shares with everyone else. Initially, they rotate the dinners between their houses.
The friends start telling their friends, and it's agreed that friends of friends can participate, but they all have to bring their own dish, and you have to host one of the gatherings.
It isn't long before you discover a problem. Nobody has a house big enough to host the dinners!
So you get the idea of renting a local community center to hold your pot-luck dinners. People continue to bring their own dishes, but now everyone is asked to pay their share of the cost of renting the hall. Not only that, but people are expected to help set up the chairs and tables and share in the labor of cleaning up the hall afterwards. Everybody pays, everybody eats.
[Nobody is trying to make a profit. If you end up collecting more money than it cost to put on the event, the person whose turn it is to organize the event generally tries to refund part of the cost back to the people who made it happen. Sometimes, unfortunately, the organizer doesn't collect enough, and sometimes they end up having to make up the difference out of their own pocket, although it's not uncommon for other members to help take up a collection to help out the person who was out of pocket.]
Your event is now even more popular than ever. One of your group happens to know a celebrity chef. Y'all get the idea of inviting them to attend your gathering, give a talk, and maybe even cook some stuff. But that costs money, so everyone has to help pay for that. [And that celebrity is essentially a paid guest of honor and is not expected to pay/help like the ongoing members do.]
[Some of the members of your group are professional chefs themselves. They bring dishes to show off, and sometimes to talk about what they're working on. They, however, pay their share of the hall and they share in the work of keeping things working.]
Time passes. You've outgrown a local community hall and now have to rent a ballroom in a hotel. You somehow manage to get the permits for the food, but the costs are going up faster than the division of costs per person.
It's still popular, but now you have people who want to attend and eat but are not themselves particularly good cooks.
[One of the celebrity chefs, Martin George, has been bringing dishes since before he got his own television show. He likes the gatherings so much that he continues to bring dishes and pay his share of the costs.]
The members of the "Elves, Gnomes, and Little Green Men Chowder Society" (as y'all whimsically named your movable feast) decide that it would be okay to allow non-cooking members, but that everyone still needs to pay their share of the cost. (Onlookers will recognize the reference here to a historical Bay Area SF fan group.)
More time passes, and now only about half of the people attending the EGLGMCS feasts are bringing dishes. [But that's okay because there's always a lot of leftovers, and besides, the cooking members have always liked to share.] Everyone is still paying for the cost of the facilities, and there's still an expectation that everyone will help in some way.
But the newcomers (who just wanted to eat the food at this funny sort of restaurant they heard about) don't understand why they not only are being charged for their food, but are expected to help set up chairs and clean up afterwards. They've never even heard of pot-luck dinners. If you pay money and get food, it must be a restaurant, and they expect to be treated like the paying customers they consider themselves to be. Anything else is cheating them. [When the earlier members point out that they also are paying, and they're also cooking the food, setting up chairs, and washing up afterwards, the newcomers look at them like they're really space aliens, because paying and working is manifestly and obviously insane.]
Here endeth the parable.
Worldcon, the oldest continually-running science fiction and fantasy fandom event, has been organized as a metaphorical pot-luck dinner from the start in 1939. It is not a paid entertainment event, anymore than a pot-luck dinner is a buffet restaurant.