I’ve seen the other side of how this discussion makes people uncomfortable, on Twitter, where negative assumptions and bad faith abound. Yes, I know, Twitter. The day my book was released, a smattering of users who didn’t read the book attacked me for saying the industry was hidden. But given its breadth and a lack of widespread public and political attention, there is no other way to describe it.

Perhaps nothing confuses and bedevils Americans more than talking about class. It’s the thing we’re supposed to pretend doesn’t exist, doesn’t define us, doesn’t lay out the road map to our lives from birth. But we are a society organized by socioeconomic class and the intersection of racism and regionalism. All of these factors are layered within the stories of who needs to sell their blood plasma to make ends meet. Plasma centers proliferate in communities of color, along the US-Mexico border and in other parts of this country that are less white.

My own reasons for this project have been deeply personal, and perhaps a tiny bit selfish. I rely on the plasma extracted from other people, their proteins spun into a medication that has for 20 years kept me from serious disability. Knowing it’s a business that thrives on people’s economic hardship comes with no small amount of guilt. It might seem against my own self-interest to write about this business and the way it preys upon the cracks in American society. But ignoring our tangled and growing class divide won’t make it disappear.

Blood Money: The Story of Life, Death, and Profit Inside America’s Blood Industry, is out now