Pope Francis tweeted, “Inequality is the root of social evil.” The pope is worse than wrong.
In a free market—a market in which government consistently protects people’s rights—some people earn more than others do, a relative few earn vast fortunes, and each individual is free to keep, spend, or give away what he earns according to his own judgment. One consequence of government protecting people’s rights is that people are unequal in how much they earn and own.
Steve Jobs, Michael Dell, Charles Koch, and the Walton family (among many others) amassed huge fortunes by building enormously successful businesses that provide customers with valuable goods and services. Many people work hard in school, strive to excel in their careers, and invest their wealth prudently; and, of course, they usually amass more wealth than do those who slack off, collect welfare rather than work, and squander their money.
Government can curb or eliminate such inequality in only two basic ways. Government can forcibly seize some people’s wealth and give it to others, or government can forcibly prevent some people from earning or acquiring more wealth than others. In other words, government can curb or eliminate such inequality only by initiating force and thus violating people’s moral right to earn and use their wealth as they see fit.
Of course, when and to the degree that government violates rather than protects people’s rights—as by redistributing wealth and violating businessmen's rights to do business—some people obtain wealth not by productive effort but by force (whether direct or indirect). In some such cases, one consequence is more inequality—in that some end up with more resources than others have. (Thomas Sowell offers an example of this.) In such cases, the resulting inequality is indeed unjust—and the fundamental cause of the injustice is government’s violation of rights.
In sum, inequality of resources per se is neither good nor bad. When government protects people’s rights and some people earn more wealth than others do by their own productive effort, the outcome is just. When government (or a criminal) violates people’s rights, the outcome (not to mention the act) is unjust—whether the result is more inequality or less.
Contra the pope, the root of social evil is not inequality but initiatory physical force. As Ayn Rand observes,
Man’s rights can be violated only by the use of physical force. It is only by means of physical force that one man can deprive another of his life, or enslave him, or rob him, or prevent him from pursuing his own goals, or compel him to act against his own rational judgment.
By calling inequality evil regardless of context—such as who earned what and who didn’t—the pope calls indirectly for the initiation of government coercion. The evil here is not inequality but the pope’s sanction of force.