If there’s one thing the media loves, it’s a nice round number. Unlessyou had chosen this week to play Henry Thoreau, you probably noticed thatthe United States population passed the 300 million mark at some pointin the last few days. Local newspapers rushed to declare one of theirown the 300 millionth soul and nearly every media outlet from NPR to CNNto The News Hour devoted air time to explain to the their viewersWhat It All Means.

All the attention brought into high relief just how absent demography isfrom our routine political discussions. Well, with some notableexceptions. On October 18, I got an e-mail from the Federation for AmericanImmigration Reform (FAIR) with the subject “300 Million and Counting!”–complete with the obligatory black-and-white photo of a crowded citystreet at rush hour: Hell is other people. “Can the US sustain thiscontinued increase in its population or will this growth suffocate aonce thriving nation?,” the e-mail asked. It wasn’t really a question.

It’s a strange quirk of the anti-immigration movement, that while thebase is animated largely by xenophobia, the leadership, like FAIR, Numbers USA and others aredriven by the far more esoteric concern of population growth. Much ofthis is the legacy of John Tanton, the eccentric, brilliant opthamologist from Petoskey, Michigan who founded FAIR and pretty muchsingle-handedly started the modern anti-immigration movement. Tanton’sworldview was formed at a time when demography was a major concern,thanks to Paul Ehrlich’s landmark book The Population Bomb, whichpredicted the world was about to breed itself out of existence. As theUnited States’ native-born birthrate leveled off in the 1960s, Tantonturned his attention to the source of the nation’s continued growth,which was propelled by immigrants and their offspring. The rest ishistory.

So that explains why Dan Stein, head of FAIR, was everywhere last week,from MSNBC to the op-ed pages of USA Today making the case that300 million was an ominous milestone and the culprit was our porousborders. For FAIR, the rare spotlight on population growth was a goldenopportunity to make their case. “Overcrowded schools, congestedhighways, environmental stresses: We are a nation paving over itswildernesses while depending on our enemies for vital resources,” Steinwrote in an editorial in USA Today. “Why? Because Americans havebeen blindsided by a government-mandated mass immigration program that’sfueling this nation’s runaway population growth. This growth was neitherplanned nor expected, but we feel the consequences every day.”

Stein’s partly right. There is little official policy that sets out anideal US population, but images of crowded streets and traffic jamsaside, the fact remains that the US is still a very big place, andrelatively sparsely populated. With thirty-two people per squarekilometer, the US ranks 172nd in the world in density. Amsterdam andSouth Korea, just to name two, are each more than ten times as dense.

But of the world’s richest nations, the United States is also the onlyone with a robustly growing population. Most of Europe has been caughtin a much-discussed population drought, a birthrate so far belowreplacement rates that countries like Italy and Spain could lose halftheir population in the next fifty years. But thanks largely to higherbirth rates of America’s immigrants, the US faces no such problems.

Is that a good thing? There are arguments on both sides, but ultimatelyit’s the wrong question. Some in the anti-immigration movement point outthe environmental effects of the increased resource consumption comefrom increased population, but if that’s your concern, there’s no reasonto wall off the United States and let, say, Mexico slide intoenvironmental ruin. And while it’s true that once people come to the USthey burn a lot more carbon, that logic would also imply that it’s agood idea to keep the rest of the world poor, which doesn’t quite seemfair. The fact is that population growth isn’t really a problem for theUS. As one environmentalist told me, “It’s not that we have too manypeople–we have too many cars.”

Of course, you can’t very well win elections or raise much money demonizing cars. Groups like FAIR figured that out long ago.