The money isn’t in the market, when you buy shares the money goes to the seller.

Money in this context is just proxy for value. You have exchanged cash for an equal value of stock. After this either could go up or down in value as the market determines. Sometimes the market doesn't like one kind of cash even and that value can reduce. On the other hand, if everyone is invested into a certain kind of cash then it's unlikely that cash would ever lose its value. Stocks have to work the same way fundamentally. The difference so far has been the volume at which these transactions happen. But since 2008, the volume of stock transactions has been growing exponentially. Has it crossed a critical mass ensuring its value will be propped up for a really long time?