These days, overpopulation is primarily a hang-up for environmentalists, though suburbanites and feminists occasionally whine about it, too. And an important part of the argument has changed. While before, Progressives were worried about the "muck" at the low end of the global population, they're now vexed by the fat cats at the top.
Americans consume more of the earth's resources, they complain, and produce piles more greenhouse gasses. At the environmentalist fringe, there's even a growing movement to convince eco-friendly Americans to voluntarily reduce or eliminate their own reproduction in order to ease the strain on Mother Nature. Since the political orientation of your parents is the single best determinant of your own politics, you can expect a lot fewer environmentalists in a couple decades if this idea catches on.
What unites today's worriers and those of yesteryear is their common allegiance to Malthusianism. The British economist Thomas Malthus argued that population will always outstrip available resources. And he was 100 percent wrong.
Because people are, in the words of Julian Simon, "the ultimate resource." Given the right policies, intellectual and economic productivity trumps biological reproductivity. "Between 1820 and 1992," Ronald Bailey writes in Earth Report 2000, "world population quintupled even as the world's economies grew 40-fold." Productivity matters more than other statistical measures because it demonstrates we're doing more with less. That's why, for example, starvation is a political disaster, not a natural one. There's literally too much food in the world. There's also plenty of land left. You could move the entire world population inside medium-sized homes and they'd all fit inside Texas, yielding a population density similar to that of Paris.
Today's Malthusians still look askance at economic productivity, believing that it's better to limit growth at a "sustainable" rate, which means consigning billions of poor people to lives that threaten the environment (poor people treat their environments like expendable resources rather than priceless luxuries) and, worse, threaten their own lives. It's more enlightened than dreaming of a giant gas chamber, to be sure. But that's got to be small solace for those trapped at the bottom.