Martin Luther King, Jr. called it "the modern plague" and challenged us to heal it, especially since we knew how.That "plague" is overpopulation—but in Dr. King's time, U.S. population was driven by a high birth rate.Today, the major driver of U.S. population growth is mass immigration—up to 1.5 million people come to live in the U.S. every year, and have for years, through legal and illegal means.

What does that have to do with the environment? Well, the last thing this planet needs is more overconsuming Americans, says environmental ethicist, author, progressive activist, and philosophy professor Dr. Philip Cafaro. Mass immigration is also the last thing needed by the poor people already living in America: it forces lower wages and more competition for low-skilled jobs. Yes, immigrants themselves can often build better lives here. And hey! Wealthy Americans and corporations get cheap labor and new markets.

Phil Cafaro's excellent book, How Many Is Too Many?: The Progressive Argument for Reducing Immigration Into the United States, lays out sane, humane arguments you've probably never heard before. Too often, US immigration is talked about in a binary, polarizing way: you're a liberal for open borders, or you're a conservative who wants a wall. It takes on racial tones—you're either for poor people from other countries building a better life in the U.S., or you fear a changing demographic and retreat into nationalism. But what if…

-You care about the serious environmental impacts?-You realize the connection between a "perpetual growth economy," which screws the planet, and the drive for more immigrants to work more cheaply and buy more stuff?-You understand how mass immigration drives economic inequality in the US?-You want to help the world's poor in a way that helps them build better lives in their own countries, cultures, and communities?-You realize the world has changed since Emma Lazarus wrote that poem?-You yourself are the descendent of immigrants and don't want to be selfish?And what if you wonder why the hell environmentalists don't talk about the impacts of immigration anymore, when it used to be a major issue?

This conversation, and Phil's book, outline not only the problems, but suggestions for building better immigration policies: Open to refugees, home to Dreamers, but at a scale our biosystems can handle. Any "developed" country could benefit from his work.

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