Adjusting the arcane rules governing exchange trading execution will not remedy broader financial-system problems and global macroeconomic mismanagement that are producing a new wave of volatility in the world’s securities markets.

Volatility in the world’s stock markets has increased again since the end of April, after about six months of relative tranquility.

In this environment, and with the memory of 2007-08, investors and regulators are wary of the possibility of unexpected market moves snowballing into large and