Someone has to pay for the resources. If you're going to compete with Facebook, then someone has to pay for billions of dollars worth of infrastructure. Voluntarist P2P can work to an extent when everyone donates their computer to the task, but a better way is to allow people to pay and let experts run the nodes. People get better quality service, and experts can make a living by providing the service.

Voluntarist networks can't guarantee quality of service. You just get what you get. If you want to have 1 Gbps downloads and 100% content availability, you have to pay someone to provide that.