With the immigration debate heating up — and a federal court case over Arizona’s SB 1070 brewing — you’d think that the U.S. was besieged by growing numbers of illegal immigrants. But you’d be wrong.

Despite the heightened rhetoric and the bloodcurdling vitriol surrounding the issue, illegal immigration has actually declined significantly over the last few years. While journalists like to characterize the anger over immigration as a response to facts on the ground — i.e. people are inundated and incensed — the numbers don’t bear them out.

In fact, the opposite is true. According to a February report by the Department of Homeland Security, the number of illegal immigrants living in the U.S. actually dropped by a whopping 1 million between 2008 and 2009, which amounts to the sharpest decrease in 30 years. It was the second year of declining numbers.

Likewise, the Border Patrol reports that apprehensions are down by more than 60% since 2000, to 550,000 last year, the lowest number in 35 years, even though the border is more tightly controlled than ever. As William Finnegan wrote in last week’s New Yorker, “The southern border, far from being ‘unsecured,’ is in better shape than it has been for years — better managed and less porous.”

And there’s more. Despite the drumbeat about hordes of undocumented Mexicans who have come north to take our jobs, consider this: According to the Pew Hispanic Center, between 2005 and 2008, the number of Mexican migrants arriving in the U.S. actually declined by 40%.

It’s not only the number of Mexican illegal immigrants that has dropped. The fact that the U.S. economy is struggling has discouraged high-skilled immigrants from around the globe from looking for jobs in America, and the flow of applicants for H1-B visas, or work permits, has slowed. Before the recession, the entire 85,000 H1-B annual quota would be filled within days of the application date on the first of April. For fiscal year 2010, the quota wasn’t reached until December 2009.

Finally, the Census Bureau’s American Community Survey last fall revealed a historic decline in the percentage of U.S. residents who are foreign-born — from 12.6% in 2007 to 12.5% in 2008. That represents only about 40,000 people numerically, but it is the first time since the 1970 census — 40 years ago — that the foreign-born percentage of the U.S. population has gone down.

So, in the face of all this data showing that legal and illegal immigration is down dramatically, what’s all the fuss about? Why has the debate turned so nasty? Why does it seem worse than it did in 1994, during the debate over Proposition 187, California’s anti-immigrant ballot measure?

The easy answer, of course, is that the economy is tough and historically people have looked for targets to blame for their feelings of impotence.

But today I think there are other contributing factors. The political discourse overall is pretty horrific, and while immigration has always brought out the worst in people, today’s polarized climate only makes matters worse.

Furthermore, the right wing, where much of the anti-immigrant frenzy comes from, no longer has an authoritative voice of reason pressing for decency on the issue. Four years ago, after President George W. Bush unsuccessfully launched his own effort at comprehensive immigration reform, he warned against “harsh, ugly rhetoric.” Today, Bush is hardly heard from and the right has an “open borders” policy on over-the-top rhetoric.

Struggling newspapers seeking to engage readers at any cost are also part of the problem. Whereas racist rants were once confined to marginal websites, today many papers — including this one — have opened their online comments section to, well, complete nut-jobs. Allowing vitriolic racial rhetoric to remain on a mainstream website is to give it a level of acceptability. Just last week, in response to my column on the so-called burka ban in France, a rabid commenter proposed that all those crossing the U.S.- Mexico border without papers should be shot on sight. Nice. Such “dialogue” not only pushes out reasonable people, it emboldens the unreasonable ones. By allowing it to be posted, newspapers are presiding over the mainstreaming of anti-immigrant hate speech.

There may be those who see hatred as a justifiable means to an end. Perhaps they hope that all this harsh rhetoric will keep even more illegal immigrants at home. But they’d be silly to think that such invective only makes life harder for immigrants. Unfortunately, it also actively degrades our culture, our public square and our democracy.

grodriguez@latimescolumnists.com