HFT is a different thing from what is being discussed in this thread. With HFT you're talking custom ASICs running within light-nanoseconds range of the target exchange. Ocaml very much isn't in this picture. This is about human-speed trading. Which also provides liquidity and correction of instrument prices towards their fair value, just at a different level.
The societal value of either is debatable all the same, mind you. It's more that wherever you have markets, you have money-making opportunities that can be leveraged, and therefore are.