If prices are out of line, that definitely seems like a place where automated trading would be valuable. But HFTs' tech advantage isn't just about finding a better arbitrage algorithm or being smarter: it's also quite clearly about exploiting a pure technical advantage over other traders. The fact that HFTs are so willing to invest in speed even to achieve a tiny advantage over other HFTs kind of gives the game away.

And when people quite rightly observe that having a speed advantage over other traders obviously allows extractive behavior like frontrunning, a bunch of people on HN come out with irate counter-takes that claim HFT are an unalloyed good -- never something nuanced like, "yes HFT could allow for some extractive behavior, but it's counterbalanced by these advantages which I will explain in detail." (And the corollary, which is an explanation of "why a world where all traders have the same speed advantages wouldn't have all the claimed advantages of HFT but be even more efficient.")

I guess it's also worth pointing out that these responses are usually from people who are involved in the HFT industry in some way, and usually they start out by accusing people of "not understanding the industry". Which is precisely the accusation many make against HFT: that it's so deliberately opaque that people outside the industry can't possibly determine how much extraction there is compared to value being added. Saying "trust us" or "you couldn't possibly know because you aren't on the inside profiting from it" is not the compelling argument you think it is.