[akira2501]

> but making spreads narrower does mean less money goes to middlemen.

On individual trades. I would think you'd have to also argue that their high overall trading volume is somehow also a benefit to the broader market or at the very least that it does not outcompete the benefits of narrowing.

[jeffreyrogers]

Someone is taking the other side of the trade. Presumably they have a reason for making that trade, so I don't see how higher volume makes people worse off. Probably some of those trades are wealth destroying (due to transaction costs) but it is destroying traders' and speculators' wealth, not some random person who can't afford it, since if you trade rarely your transaction costs are lower than before HFT became prominent.