Digital goods don't have zero value. We know this because people are willing to pay for them. They just have very little cost to reproduce/transport which results in easy sharing. They're not even unique in this regard - you'll find the same easy reproducibility in books, architectural plans, art, simple circuits, manufacturing techniques, algorithms... any idea that can be expressed and transmitted easily. The problem isn't that those things are worthless (they're not), it's that knowledge can't be "owned" like physical items.