> Lots of things are illegible to the public. Explain to me all the processes involved in building the smart phone in your pocket. You can't. I can't. Probably no single person in the world can. Who cares?

That's not true, not like HFT anyway.

First, you can quickly and succinctly describe the traits and benefits of a smartphone. You can be high-level at first, you don't have to explain how every detail works. There's no question, for example, that a touch screen doesn't actually work as advertised. You can just say that a smartphone is a cellular/wireless computer device with a usefully large touch-screen display.

In contrast, the unknown question with High-Frequency Trading is: is it actually providing value to anyone but the traders themselves? They might say they are "market-making" but are they really market-making (a trading role with proven market value) or are they merely exploiting structural inefficiencies in the trading infrastructure that mostly hurt everybody else? Maybe they are, but they should be able to describe it in a high level terms first (market-making, liquidity, etc.) where their role provides an obvious benefit to the market, and if you don't understand the high-level terms (eg liquidity) you can look them up.

So far as I can tell (and I am willing to be proved wrong here) there is no consensus answer to the question of whether HFT is actually valuable to markets.