I don't disagree with the assessment, but I think it might be orthogonal to the issue. I think it's very hard to monetize engagement, period, even if it's all positive, constructive, and intellectual engagement.
If your service's business strategy is "1) acquire hundreds of millions of users and charge them all $0.00 per year for many years, 2) acquire lots of expensive infrastructure and employees to support the service, 3) ???, 4) profit", it's not going to be easy.
If your service's business strategy is "1) acquire hundreds of millions of users and charge them all $0.00 per year for many years, 2) acquire lots of expensive infrastructure and employees to support the service, 3) ???, 4) profit", it's not going to be easy.