This is a straw man. I cannot think of anyone (and I'd love to see you find a progressive or anyone) that would say that economics is a zero sum game.
A lot of this community did form around pg's essays. However, it's a little sickening to think that anyone would take them as gospel. Since the early days of reddit and hn these things have been vigorously debated. pg is at his best when talking about start ups and I think the way he conveys how founders should think is good stuff. However, please do not expect, or treat his writing, like he will win a nobel prize in economics.