One might think that a “socialist market economy” would feature markets that are less prone to booms and busts than the U.S. Not exactly.

As longtime China watchers know, the country’s still-immature markets are in many ways more bubble-prone than their Western counterparts, thanks to heavy involvement from retail investors who often take cues from government policy, rather than quaint notions like earnings. Tanking Chinese stocks—the Shanghai Composite is now down nearly 25% from its January peak—could therefore be taken...