Not true. Your trading provides a secondary market for companies. It encourages people to create new companies to later sell to investors.
Further, you get rewarded to the degree that you correctly speculate on the future prices of stocks (or whatever you trade) and penalised when you get it wrong. That tends to bring future prices back in time (that is, speculation causes the price of something to reflect today what it otherwise would have been in the future). That's really important because it causes capital to be more accurately alloted to ventures that will be creating value in the future and away from those that will create less value or be destructive of value in the future.
Further, you get rewarded to the degree that you correctly speculate on the future prices of stocks (or whatever you trade) and penalised when you get it wrong. That tends to bring future prices back in time (that is, speculation causes the price of something to reflect today what it otherwise would have been in the future). That's really important because it causes capital to be more accurately alloted to ventures that will be creating value in the future and away from those that will create less value or be destructive of value in the future.