I do get the value of trading, investing, and some form of arbitrage. Heck, I don't have to search for the farm to get my milk. That's a service, and it does deserve a reward. What the author did is a bit different:
> Most of the market volume was other bots that would only execute a trade with me if they thought they had some statistical edge.
I understood it meant "they would trade with me only if they think I was the sucker". And of course, he would trade with them only if he thinks they were the suckers. It's not providing a service. It's fighting in a zero-sum economy.
Now he did say "most of the market volume". So there's a fraction that's not bots, and probably also a smaller fraction that does not even play the zero sum game, but instead does some positive-sum trading with the mostly-zero-sum players. But this interface boundary seems incredibly thin, compared to the internal zero-sum behemoth. That looks like a highly inefficient use of time, energy, and brains.
And even then, I'm not sure the zero-sum game provides any service to the rest of the world: zero-sum players base their models on the behaviour of each other, not on the actual performance of companies. That would add no new information to the system. At best, that only amplifies the effect of the few that actually predict company performance. And I doubt it does it well.