> Meanwhile, all this stuff costs money, people, resources that aren't available for actual productive work instead of overhead.

That's a very high standard. What's productive? What's productive enough, in your book, to be worth the effort used here?

Median productiveness is plenty, assuming this is not productive activity.

But what's "productive?". Farming? Manufacturing? What if the farmed food is unhealthy? If the manufactured good is wasteful?

My view is that current liquidity and pricing are far from perfect, particularly when it matters most (e.g. a market panic) and particularly in the global context of the vast universe of interrelated instruments that need better relative pricing. Given that we benefit from realtime pricing, milliseconds matter when you must determine a large vector of prices with complex dependencies using the ensemble recursive system that is the global market.

> My view is that current liquidity and pricing are far from perfect, particularly when it matters most (e.g. a market panic)

And in a market panic, your friendly HFT shop next door is there and offering to buy and sell to stabilise the price?

> Given that we benefit from realtime pricing

Yeah, if you assume the conclusion that we benefit from it, then we do. But have you shown this?

In which market do we benefit from milliseconds pricing, compared to, say, an auction every minute?

> And in a market panic, your friendly HFT shop next door is there and offering to buy and sell to stabilise the price?

Some are. It's not that they are friendly, it's just that doing so can be highly profitable if one can estimate the mispricing with a sufficient degree of certainty.

> In which market do we benefit from milliseconds pricing, compared to, say, an auction every minute?

I argue that all of the significant ones benefit. The global market is huge and interrelated in complex ways. There are many trading entities with a variety of specialties. They communicate their expertise through the markets by placing orders. It's an iterative process and a lot of information must be conveyed. The faster the entities can communicate back and forth, the more accurately the prices can represent a weighted consensus. Constraining the trading to 1 minute auctions would reduce the communication bandwidth.

>that aren't available for actual productive work instead of overhead.

That’s a very biased view. Another view would be that improving the efficiency of the largest markets in the world have a much larger positive impact on society than the vast majority of the “productive” work you refer to.

It's biased to the premise, which is that "day trading's" contribution to price efficiency & liquidity are of diminishing value, and that the marginal value is essentially 0 or negative.