I think you're confused about how HFTs create value. They create value because they're the first ones to make a market in something. They send out limit orders

I think you're confused about how HFTs create value. They create value because they're the first ones to make a market in something. They send out limit orders in every product. An investor then sends a marketable order to the exchange that fills one of the HFT's resting orders. If the HFT wasn't there then the investor's order would just fill a bank's order that would probably be wider and wouldn't respond to changing situations as quickly. The innovation is that HFTs are able to make better markets with fewer people. This means that less money ends up in the pockets of intermediaries and more money stays in real investors' pockets. Are HFTs always doing the right thing? No of course not, but HFTs are pretty clearly some of the most ethical firms out there.