Can't you say that about any other asset? If I sell my house for more than I paid for it, it's zero sum since someone simply provided me that money. But that's not how we determine value. It's positive sum because the buyer attributes a value higher than he had paid for it, otherwise he wouldn't have bought my home to begin with. You can say no one can reasonably "value" a crypto currency, but there's 100+ billion dollars that says otherwise.
> There is no silver bullet, but there are a lot of things that can throw sand in the gears, degrading Bitcoin and other systems into unusability.
Ironically, the author goes on to describe a way to attack the value of Bitcoin and presumably drive its price down (destroying value). So it doesn't seem zero sum after all