It should be obvious how it is beneficial. HFTs are in competition with themselves, not with investors like you and I. Prior to HFT market making, manual market

It should be obvious how it is beneficial. HFTs are in competition with themselves, not with investors like you and I. Prior to HFT market making, manual market makers (brokers on the floor) were making huge profits on large spreads. This means worse prices for the average investor. Without HFT there would be no "1 penny" spread.