[traK6Dcm]

HFT may not, but trading itself definitely provides positive value. People's utility function is not purely monetary over an infinite time horizon. Trading allows you to trade off price and risk over multiple time horizons.

For example, a trade where someone needs to convert his assets into cash due to a family emergency benefits both sides. The person with the emergency takes liquidity from the market and pays a premium because the trade is time-sensitive - he needs cash the next day. Other liquidity traders may profit from such "uninformed" flow in the long term, but both parties are happy because they got what they want.

Another example is trading off risk and hedging against certain changes in the world that would affect you.