Until you are like in HK and need to organize yourselves for some reason.

> If we're not going to pay with dollar bills, we pay with privacy.

Paying with ads is also possible.

But if you pay with ads, don't you need to see a LOT of ads, unless your privacy is compromised and they use trackers about you to give you targeted (i.e. more lucrative) ads?

I don't see why topic-based ads based entirely on on-site participation would be a problem. No need for any user-hostile garbage, bucket your communities into topics, and let advertisers target the topics or the intersections between them. Ads are sold on-site, not via third party networks.

Reddit does this, but no idea how successful it is.

I'm not sure what it costs to have a service running and what non-tracking adds may yield nowadays.

So: not sure.