Earlier quoted context omitted.
This is a pretty loaded question to then say "not trying to be judgemental"...take out the bias if that's actually the case: "What kind of benefit do you believe your work provides to society?" or "How do you justify the extra resources taken away from society that may be more beneficial elsewhere, such as X?"
Well I don't know how to make it less loaded x) It's just how things are, it's a work that does no useful work in any meaningful sense, but serves to make some already fabulously rich people even richer (in fact, it extracts that value from non-HFT traders, so even those are shafted here). My point is that I'm curious regarding how the people who work in these things feel about their job. Do they think they're doing…
His job facilitates trades between people who want to trade with each other. Since they are part of society, our society benefits from his work.
Evidently it's doing more than "make some already fabulously rich people even richer", because it's paying salaries for some programmers, as well.