That's discussed in the article though. The open world assumption is untenable. Having shareable interoperable schemata that can refer to each-other safely would be a god send however. And that's what is currently very hard but needn't be.
Whether you trust the URIs or the data that was placed there is not a problem for the semantic web. The fact that you _can_ state these things and relate to other resources and concepts on the web is already wonderful and useful in itself. Google is reading this metadata and relating it to their trust/ranking-graph. The semantic web 'community' could do the same later also, in a more decentralized way (blockhain web IDs perhaps?). For now it all works fine.
