Full disclosure: 1) I think HFT has brought nothing good to the world. 2) I'm of the opinion that stock trading in general should be illegal. THAT SAID: If I were to list "immediate existential threats to the modern world" I would not include HFT. Yeah, the flash crash was no bueno but it was nothing compared to, say, LTCM. Yeah, algorithms can manipulate the market but nothing compared to, say, Enron. And yeah, a lot of money can vanish in the stock market if things go wrong but it's a fly on the ass of the elephant that is the bond market. Quoth Michael Lewis, comparing his book The Big Short with his debut from 20 years earlier, Liar's Poker: I mean, the editor in chief of Business Insider, Henry Blodgett, is only an editor because he's been banned for life from trading because of manipulating investors. Clearly, that worked out poorly for him. So yeah - the algorithms fuck up. But humans fuck up worse, they fuck up consistently, and they often fuck up on purpose.…exactly twenty years after Howie Rubin became a scandalous household name for losing $250 million, another mortgage bond trader named Howie, inside Morgan Stanley, would lose $9 Billion on a single mortgage trade, and remain essentially unknown, without anyone beyond a small circle inside Morgan Stanley ever hearing about what he'd done, or why.