If someone buys stock for $100 and sells it for $10 dollars. How much money is lost in the world? answer: 0$
You make a good point. There is a difference between being lost in the stock market, and being lost overall. BUT, if say I had holdings for a stock that was valued at $100 on December 31st, that is NOW valued at $10, I would say that there is a substantial difference in the total value of wealth in the world.
Not quite true. When the stock drops from $100 to $10,
the capital value of that stock drops by $90 x number of shares outstanding. While it is true that only a small fraction of outstanding shares get traded, the trading price DOES AFFECT market capitalization, and that paper loss affects brains of consumers.