as far as I can tell, HFT shops aren't producing anything tangible. Considering almost nothing is as zero-sum as a stock market at sub-second timescales, their

as far as I can tell, HFT shops aren't producing anything tangible. Considering almost nothing is as zero-sum as a stock market at sub-second timescales, their revenue is exactly equal to the costs for other market participants. For Virtu Finance, mentioned by another comment, that's around $800 million/year. That's not really that much in the scheme of things, but it's only one company, and I doubt the other investors would be willing to spend similar on insurance against volatility.