“Creative destruction” is Mitt Romney’s best defense for his career in private equity and the trail of displaced workers some of his ventures left behind. The idea comes from the economist Joseph Schumpeter, who argued that capitalism generates economic growth through “gales of creative destruction” that sweep away obsolete technologies and products. As Romney’s advocates have it, that’s what his firm, Bain Capital, has advanced—painful economic changes that are essential to a rising standard of living.