The Hawthorne Effect, Is It Really Free?

The utility of the network is tied directly to how many people are on it. If you add people, if you charge people for that, you add friction to them joining. So at least at the start, it needs to be free. But even if you get to a terminal value where you have everyone signed up, if you then put up a paywall, you're going to lose people and again reduce the value of the network. You're going to open the door for a competitor. And so the question is, is there a way of building something like this that doesn't require advertising?