Just because you don't understand the value something provides, it doesn't mean that it doesn't provide it.
I don't think the argument is that these optimisations don't bring value; it's that they don't bring as much value to society as an effective cancer treatment, or a new technology that cheaply and cleanly purifies water, or [insert other breakthrough here].
I think it's more about the ratio of value created vs. value extracted. Sure, more efficient markets create some benefits for the rest of us, but those benefits are the crumbs under the market makers' tables. So we get slightly better smart phones, huh? Whoop de do. That's a benefit very close to zero. If I had to choose between a new smart phone and one scoop of good ice cream, even for an equal price, I'd go for the ice cream. On the flip side, for that "amazing increase in market efficiency" quite a few financiers end up making nine or even ten figures. Which part of that really motivates them? Which part has a greater effect on society (a negative one BTW) ten years from now?
People who dismiss the value of complex derivatives and HFT and other Wall Street shenanigans don't necessarily lack understanding, and it's obnoxious to say so. They just add perspective to that understanding. People who obsess over prices and ignore true value are sociopaths and should be dealt with as such.
I don't think the argument is that these optimisations don't bring value; it's that they don't bring as much value to society as an effective cancer treatment, or a new technology that cheaply and cleanly purifies water, or [insert other breakthrough here].