Thompson's point here isn't about the content itself, but rather the supply chain for the content. Because the internet effectively provides 'infinite' distribution, the traditional models of controlling distribution are worthless. This is a very consistent theme in his writings.
Consider that both the worthless and valuable content that you've defined use the same methods for distribution; Facebook, Twitter, Google, etc.
Consider that both the worthless and valuable content that you've defined use the same methods for distribution; Facebook, Twitter, Google, etc.