What a great question. I do think that, generally speaking, confidence that the markets are stable is good for an economy, and these sorts of events undermine that confidence.

It's important not to understate the cost of failure in these markets. A firm might go bankrupt and have to lay off real people if caught on the wrong side of such an event.

I also think that there is a direct connection between events like the Flash Crash and things like Nasdaq's mishandling of the Facebook IPO, which, again, had real costs in terms of time and money. Both emerge, I would argue, from a similar flavor of complexity.

I'm struggling for an analogy to show that it matters. Maybe it's a little like Target's website going down. It's not Quality, in a Zen and the Art of Motorcycle Maintenance way, even if it's only down for a short time, and the consequences were "only lost orders." Compelling?