Pleas don't spout out 'zero sum' like you think it means something insightful here. Any marketplace is 'zero sum' if you think about it. There's a buyer and seller. So what?
Marketplaces are not at all inherently zero sum games. Wikipedia's definition (which is a fine one) is: "a participant's gain (or loss) of utility is exactly balanced by the losses (or gains) of the utility of the other participant(s). If the total gains of the participants are added up and the total losses are subtracted, they will sum to zero."
The key thing here that is is measured in utility (not in the price of the good). Of course every trade or transaction is flat in that I sold it to you for the price you bought it at (that is obvious and non-what a zero sum game means). The issue is whether we are both made better off or not.
If I don't want to bear the risk of holding bitcoins and am happier mitigating that risk by selling them for dollars, my utility increased. Similarly, if you purchased them from me because you want to bear such risk, your utility increased. Even removing the risk/uncertainty from the equation, my willingness to pay for a good is not the same as the market price. Thus, if I sell bitcoins bc my value of them is less than the current market price, then I am improved. Similarly, if you value bitcoins above the current market price and buy them from me, then your willingness to pay was higher than the price you paid. Thus, you have significant consumer surplus from that trade.
There are called pareto efficient transactions. Most transactions are actually pareto efficient where at least one of the individuals increased their utility and no one involved in the trade decreased their utility.
This excerpt does a good job articulating this: "Specifically, all trade is by definition positive sum, because when two parties agree to an exchange each party must consider the goods it is receiving to be more valuable than the goods it is delivering. In fact, all economic exchanges must benefit both parties to the point that each party can overcome its transaction costs, or the transaction would simply not take place."
For example, futures and options are zero-sum because every dollar of profit that one trader makes is offset by a dollar of loss from another trader.
But stock markets are not zero-sum. Prices can be bid up without a single share changing hands, creating new wealth out of thin air, and everyone wins. Conversely, prices can go to zero, destroying wealth and making everyone a loser.
Same thing for most other markets you can think of, from real estate to used cars to your local flea market. As with bitcoin exchanges, none of these are zero-sum since there doesn't have to be a loser for every winner.
A more compelling argument against zero-sum is that traders and investors have different time frames and objectives. And, indeed, the classic argument in the futures market is that a farmer who buys a hedge from a speculator represents a potential positive outcome for both.
I just made a 20x return on my investment, and you own 50% of a great opportunity. Who's the loser here that makes this a zero-sum market?
Our autonomous flying cars go into production, and now your 50% is worth $100 billion, and you sell your shares to Elon Musk. Where's the zero sum?
Second, zero sum requires a definition of utility for each participant. If those definitions vary (and they almost assuredly do) then a reasonable argument can be made that to define whether the activity is a zero-sum game or not requires a commonality amongst those utilities (dollars, for example). This is often not the case in trading (for example, the farmer hedging his crop with a speculator who seems to profit short term).
Again, not saying you're wrong, but your example is useless.
vs
>I'm not arguing that it is zero-sum
So, what are you saying there then.
Now I've unintentionally started an argument about what is / is not zero sum and what bits of a market you take your definitions from. That was the exact opposite of what I was trying to say. If it is zero-sum, why does that even change anything or make the trading (from the original paper) worthwhile or not? I'm trying to say that 'zero sum' or not, it changes nothing and gives no additional insight.