There’s been plenty of talk about the radical right lately, involving both the United States and Europe. This is unfortunately necessary, as ideas we thought we’d left behind — socialism, protectionism even anti-Semitism — are back again.

But let’s not fall into the trap of thinking that the only threat to liberalism is the alt-right. Many forces on the left support some of those old, bad ideas, and they’re not all masked antifa. 

Take protectionism, for instance. The Washington Post reports that “rather than jeer Trump’s protectionist positions, Democrats are echoing them and amplifying them.” The Democratic platform in 2016 rebuked President Bill Clinton’s trade deals, and former secretary of state Hillary Clinton reversed her support for a trade deal with Asian countries.

And socialism. A democratic socialist who praised Hugo Chavez’s Venezuela came darn near defeating the Democratic party’s anointed presidential candidate. And both Hillary Clinton and Democratic National Committee Chairwoman Rep. Debbie Wasserman Schultz were either unable or unwilling to explain “What’s the difference between a socialist and a Democrat?” 

Now comes New York City mayor Bill de Blasio, a favorite among “progressive” Democrats whom New York Democratic voters easily nominated for a second term on Tuesday, to explain to a friendly interviewer that the obstacle to economic progress is private property:

What’s been hardest is the way our legal system is structured to favor private property. I think people all over this city, of every background, would like to have the city government be able to determine which building goes where, how high it will be, who gets to live in it, what the rent will be. I think there’s a socialistic impulse, which I hear every day, in every kind of community, that they would like things to be planned in accordance to their needs. And I would, too. Unfortunately, what stands in the way of that is hundreds of years of history that have elevated property rights and wealth to the point that that’s the reality that calls the tune on a lot of development….

Look, if I had my druthers, the city government would determine every single plot of land, how development would proceed. And there would be very stringent requirements around income levels and rents. That’s a world I’d love to see, and I think what we have, in this city at least, are people who would love to have the New Deal back, on one level. They’d love to have a very, very powerful government, including a federal government, involved in directly addressing their day-to-day reality.

This is mind-boggling. The mayor of the world’s financial center, the hub of American and global capitalism, thinks that the obstacle to progress is private property, the institutional system that has brought billions of people around the world out of back-breaking poverty. Thinks that politicians should determine where building should be built and “who gets to live in it.” Thinks that the people of enterprising New York City have a widespread impulse toward socialism and comprehensive, coercive central planning.

Mayor de Blasio says he’d like to have the power to determine what happens on every piece of land in the city. Other leaders have had such power, in the Soviet Union and China and Venezuela, and those systems did not produce progress. Or even toilet paper.

The Encyclopedia of Libertarianism says, “Of the different configurations of property rights, only private property provides a workable basis for a free society, a productive economy and justice.” And, “Private property restricts government power and decentralizes decision making. It confers on an individual the right to use and dispose of some good.”

That’s just what irks Mayor de Blasio: Property rights limit his power and give individuals, not him, the right to decide how to use their property.

Private property is necessary for freedom. It divides and limits power. It allows markets and trade to happen, creating economic growth. It protects freedom of the press because ideas are expressed through property — printing presses, auditoriums, billboards, audio equipment, broadcast frequencies, computer networks, web servers and so on.

Countries that have comprehensively denied private property rights have found themselves without freedom or prosperity — and with plenty of inequality. Mayor de Blasio’s ideas are deeply dangerous, all the more so because he’s not an internet troll or a perennial losing candidate but the mayor of a great city built on the foundation he wants to destroy.

Like the ideas animating the new radical right, the new radical left is embracing ideas that have brought human misery wherever they have been tried.