Financial markets are fast-moving, complex, and opaque. Even the U.S. stock market is fragmented into an array of competing exchanges and a set of proprietary “dark pools” run by financial firms. Meanwhile, high-frequency traders zoom around buying and selling stocks at speeds other investors cannot match. Yet stocks represent a relatively transparent investment compared to many types of bonds, derivatives, and commodities. So when the financial sector melted down in 2007-08, it led to a wave of reforms as regulators sought to rationalize markets. But every financial market, reformed or…
