You must be aware somewhere that both sides of every single trade are in it because they find a benefit in that trade, right? Some need the cash, some need to t

You must be aware somewhere that both sides of every single trade are in it because they find a benefit in that trade, right? Some need the cash, some need to turn cash into investments, some are changing their minds from favoring firm A to favoring firm B, etc, etc. All the way to pension funds ... doing the exact same thing. You can imagine other ways to do it (but good luck making these other ways "fair" or "efficient" or "fast") - or you can recognize that a market is an elegant (in the engineering sense) way to do it. Once you have a market, you also want liquidity. Anyone who tried buying or selling illiquid shares (or illiquid goods), knows how much of a pain is lack of liquidity. It truly is desirable.