Nearly half of millennials say they prefer socialism to capitalism, but what do they mean? “My policies most closely resemble what we see in the U.K., in Norway, in Finland, in Sweden,” Rep. Alexandria Ocasio-Cortez told “60 Minutes.” Yet Sweden’s experiment with socialist policies was disastrous, and its economic success in recent decades is a result of market-based reforms.

Until the mid-20th century, Sweden pursued highly competitive market-based policies. By 1970 Sweden achieved the world’s fourth-highest per capita income....