That’s the title of a thoughtful post by Ilya Somin on the Volokh Conspiracy blog. It’s well worth reading in its entirety, but here are a few excerpts:

Some may find it surprising that the perpetrator of the recent horrific New Zealand terrorist attack that killed fifty Muslim worshipers in two mosques, combined seemingly right-wing nationalism with seemingly left-wing socialism and environmentalism. He hates nonwhite immigrants to Western nations, but also hates capitalism and capitalists, and believes that we must take draconian measures to stave off environmental catastrophe. … But … the terrorist’s worldview is less unusual than it might seem. A similar combination of views is evident in many xenophobic nationalist movements, both past and present. Socialists and nationalists have their differences. But they also have much in common, including a zero-sum view of the world.

Anti-immigrant nationalist parties in Europe often combine hostility to nonwhite immigration with support for extensive government control of the economy. That’s true of such cases as the National Front in France (now renamed as the “National Rally”) and the AfD in Germany. Such parties often also often blame immigrants for real and imagined environmental degradation, just as the perpetrator of the New Zealand attack does. Numbers USA, one of the most influential anti-immigration organizations in the US, has similar views, including advocating coercive population control and blaming immigrants for environmental degradation. …

Some influential far-left environmentalists have also advocated coercive population control, including defending China’s cruel “one child” policy.

In the early twentieth century, the Nazis promoted an even more extreme form of racial nationalism, and combined that with even more extreme government control over the economy. Hitler advocated extermination of the Jews and the conquest of other European nations primarily because he had concluded that that was the only way Germans could survive and prosper in a zero-sum world. …

The Nazis held a particularly extreme version of the view that the world economy is a zero-sum game. But more moderate – yet still dangerous – versions of the same world-view remain common on both right and left.

Zero-sum thinking need not always lead to racial and ethnic hostility, or xenophobia. It is also often channeled in other directions, such as hostility to the wealthier members of one’s own ethnic group or society. In some cases, it leads to a combination of both fear of foreigners and fear of the wealthy.

For example, unexpectedly popular Democratic presidential candidate Bernie Sanders echoes Donald Trump’s hostility to international trade, while simultaneously arguing that ordinary Americans can only be economically successful by redistributing vast wealth from “the 1 percent.” Until recently, he also expressed considerable hostility towards immigration, denouncing the idea of free migration of labor as a plot by “the Koch brothers” and other malevolent billionaires, which would impoverish the working class and end up “doing away with the concept of a nation state.” …

Fortunately, most nationalists and socialists aren’t willing to go so far as to personally commit acts of terrorism. But all too many are willing to advocate large-scale coercion that inflicts great harm on large numbers of people, in order to ensure that they and their preferred causes don’t end up as losers in a zero-sum world. …

It would be naive to imagine that zero-sum games never occur. But they are far less common than either the far left or the nationalist right imagine. The more people come to understand that, the better.