The following story contains some basic plot spoilers for Avengers: Infinity War.

Against all odds, Infinity War, Marvel's bajillion-character epic, basically works as a film. The reason it does is Thanos, the villain at its center, is one of the best movie supervillains of all time. OK, that's not a tough title to earn—can you even name the baddies in Thor: The Dark World or Iron Man 3? Still, Thanos is an undeniably memorable character, mostly because like a lot of great evildoers his motivations are totally understandable, even close to heroic. He just takes things far enough that he crosses over into outright insanity.

Specifically, Thanos is worried that the universe is overcrowded and that this overcrowding will lead to a resource shortage and catastrophe. It's a fear reminiscent of the theories of Thomas Malthus, an 18th-century English thinker who worried that the world's rising population would result in food shortages. His calculations haven't proved to be correct, but there remain plenty of people who think that out-of-control population growth is causing environmental problems. The most drastic form this kind of logic takes is the argument that we should stop having kids in order to save the world.

Thanos takes things one step beyond calling for zero population growth—he assembles six magic stones so he can wipe out half the universe's population with a snap of his fingers. Obviously this is bad. But what about a more mild form of Thanosism, where he snaps his fingers and implements a universal one-child policy? Would we be thanking him?

To sort this out, I called up Lyman Stone, a economics researcher specializing in population issues who has written on the subject before in Vox, among other places. We had a conversation that went from Thanos to climate change to the abuse people who have lots of kids get then back to Thanos. Here's how it went:

VICE: Let's start off with a simple one: Are there too many people in the world right now?

Lyman Stone: No.

When people talk about overpopulation you have to ask, "Why? What is the problem with the number of people that we have?" You get a couple answers. Sometimes people say we can’t feed them all. That’s not true. The caloric output of current agriculture is more than enough to feed everyone, and most of the world is nowhere near maximum theoretical yields with even current technology.

Maybe people think we don’t have enough water. Water stress is a big deal in many parts of the world—but water is renewable. You can desalinate it, you can collect it from the atmosphere, it literally falls from the sky. But then you get to the problem with desalinating water for everyone, which is energy. That is the fundamental population problem—not food, not crowding, the only real issue is energy. Then the question is, why do we not have enough energy? That gets to fossil fuels, global warming—but at the end of the day, there is a vast amount of energy available using fairly simple technologies like wind, hydro energy, and biomass, which is renewable since the sun is pumping energy onto us. Energy is a place where we’re making massive strides, and the potential for renewables are enormous.

Considering all that, why are people—not just movie villains—worried about overpopulation?

Look at the calculus on global warming—global warming is caused by how much carbon it takes to produce a dollar of economic output, multiplied by the dollars of economic output per person on earth, multiplied by the number of people. The trouble is while this is a neat way to break out the problem, it makes something look causal that might not be causal, and that’s population. The question is if you reduced population, would you actually get less emissions—and the answer is not really. There’s been a lot of research on this, on what happens when you get population reduction in a society. Emissions don’t shrink nearly as much as they should. You don’t turn the power plant off because population falls 5 percent, you still have the roads, there are fixed costs that don’t change.

Furthermore, if you do the actual math—even if you assume that people are this causal instrument and that the economy would immediately respond to population changes—you come to the conclusion that there is no plausible population trajectory for the earth that makes any difference. A drop in fertility doesn’t change climate forecasts very much. It’s just not that influential, especially on the time horizon that we need. We need a change in carbon output this century to avoid catastrophic global warming. The impacts of reducing fertility start to show up in like 2075 and aren’t really big until 2200—that’s too little too late. The way you have to do it is you have to find ways to use less carbon. You have to use alternative energies, renewable energies. You have to encourage more efficient allocations of people in different living arrangements.

Everyone in the field is aware of this, but the mid-level-education, cocktail-party-level-of-information activists have it in their heads that the family with four kids down the street is causing global warming. That’s just total crap. What’s causing global warming is that your local power plant is coal-fired instead of natural gas–fired, or natural gas–fired instead of a hydro plant, or it’s a hydro plant instead of wind and solar.

Do you see that a lot, people with large families getting shamed?

It’s a real thing. I write a lot about family issues and fertility, and there are a lot of pejoratives thrown around—"breeders" is a phrase people like to use. Sit down with a family that has five or six kids and ask them what their experience going to the mall or going to the movies. The looks they get, the things that get said to them. It’s absurd what people feel they have license to say.

To get back to _Infinity War_**, can you envision a time when the world would get overcrowded? Is that a realistic concern?** Yes. There’s a thing called the Kardashev Scale, which classifies civilizations into four categories. Type 0 means a civilization that captures less than the complete energy output that reaches its planet. So the energy from a star hits your planet, are you capturing all of it? If you are, you’re type I. Type II is a civilization that captures all the energy coming out of its star—this is your science-fiction Dyson Spheres—and Type III captures the entire energy of a galaxy. We are type less-than-I, I think we’re probably close to type 0.45. That means we can probably afford to have two times as much energy consumption as we currently have and not be hitting anything like physical constraints. If we can find ways to use less energy, we can grow more. But there are physical limits. Without hypothesizing multi-planet human civilization—which we should totally do—we probably can’t sustain more than two or three times our current population. It comes down to whether we have the social will to make it happen.

In terms of planning?

In terms of policy choices that are necessary to sustain that kind of population. Exploiting all available energy sources, not wasting energy on things like non-constructive things like blowing each other up with nuclear weapons. You can only have a big population if you’re basically peaceful and your society focuses on efficiency and avoiding wasteful activities.

Would we want to live in that society? The peaceful side sounds great, but how far does society go to discourage wasteful activities? Do you have to apply to a government board to go on vacation? To sustain a large population with a good standard of living and preservation of basic liberties would require substantial technological advancement.

This is pretty far way from what Thanos is talking about. To be clear, you’re anti-Thanos, right?

Right. I am averse to solutions that involve the destruction of human life. I think those aren’t solutions. The point of making that view the villain is that it’s villainous.

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