There are a lot of advertising-funded business models around.
If we can just build a community, then advertisers will want to reach them. Will they?
If we undercut more expensive advertising media, we'll have a competitive advantage. Will you?
If we don't charge for this, our audience will accept that they have to watch some ads in lieu of payment. Even if they did, would an advertiser really be interested in reaching a bunch of freeloaders?
It's amazing how many people who talk of disrupted markets, new paradigms and constant change are so wedded to old-world solutions. Change does not discriminate. If your marketplace has changed, then all bets are off. Not just the ones you don't have to make.