Actually it's a negative sum game when you add the brokerage and taxes. Winners give a pie of there cake, losers give cake plus apple pie
Its not like if trader 1 makes a profit of x amount being long on a futures contract, then the same amount has to lost by any one trader (trade2 who gave the futures lot to trade1 who made money on it), rather it's a sum total. For the period the trader 1 holds that lot in profit, multiple traders might have entered short and then covered up.
On the other hand the people who arrange this show will always be net positive like the big investment banks, exchanges like comex, brokers and the government.
Vivek