EEK Speaks writes on Lurkers: Are Lurkers Bad?
My answer [to this]: Sometimes. Lurkers are part of a group's latent energy; good things happen when that energy is activated. Lurkers are part of the all-important weak-tie network, and it's important to keep them engaged, even if engagement does not translate to participation. However, having lots of lurkers as a community goes through its nascent "sausage stage" can hurt if it drives lurkers and other potential participants away.
With networked society, we need lurkers to help build common understanding of ideas and concepts that the "spouters" (active participants) are discussing. As EEK says, the lurkers are a critical part of the weak-tie network -- they need to understand the concepts being discussed so they can discuss them cogently with people who may be outside the network in question. And it helps to have a large common understanding of concepts, so that people can have conversations without needing to provide background.
In this sense, broadcast television is (was?) all about building common understanding across the populace. Everyone was a "lurker," but we were being informed, so that next-morning conversations over coffee had a common basis.