Here's the most amazing-but-true thing we learned this past year, something that came up last summer in the midst of arrests of allegedly illegal immigrants in Frederick and Anne Arundel counties -- one of those realities that a lot of us didn't appreciate and many others refuse (or hate) to acknowledge: Illegal immigrants pay billions in taxes.

From a column in July:

    Many Americans - I would wager, the majority of Americans - probably believe that the millions of undocumented workers are part of an underground economy that delivers no tax revenue while extracting gobs of benefits from our social services system. But most illegals pay taxes. In fact, experts believe they've paid billions in taxes and helped to shore up Social Security for the rest of us.  . . .    This explains why we don't see Internal Revenue Service agents chasing Guatemalan drywall-hangers through alleys in Baltimore.

    Since 1996, foreigners have been able to obtain an Individual Taxpayer Identification Number. Illegal immigrants have snapped up the vast majority of these ITINs and lined up to file tax returns in record numbers. "We have a financial literacy program, and every month we see an increase in applications for ITINs," says Kim Propeack of Casa de Maryland, the nonprofit group that supports immigrants here.

    In 2001, then-Fed Chairman Alan Greenspan estimated that undocumented immigrants paid about $70 billion annually in taxes and received about $43 billion in government services. Revenue has grown since then. Between 2004 and 2005, the number of tax returns filed with ITINs jumped 30 percent, according to The New York Times. There was another spike in ITINs in 2006. In 2005, the Times estimated that undocumented workers contributed about $7 billion to the Social Security system. Three months ago, the trustees of the SSA noted the importance of revenue from "other than legal" workers, many of whom are young and won't be around to collect federal retirement benefits.

    A Times editorial asked: "Would the people who want to deport all undocumented workers be willing to make up the difference and pay the taxes that the undocumented are currently paying?"

    I asked Propeack, Casa's director of community organizing, why illegal immigrants would want to get ITINs - or even phony Social Security numbers - and pay taxes at a time when the feds are trying to round them up and deport them.

    She said undocumented workers want to show a record of having paid taxes when - or if - they are allowed to apply for legal status or even citizenship. "Most [undocumented workers] hope that someday there's a program in the United States that will allow them to become citizens," Propeack says. "And they want to be able to show that they are a person of good moral character, and paying your taxes is a big part of that, one of the first things [naturalization officials] look at.

    "There are some clear areas where expenses are associated with the undocumented," Propeak says. "Emergency room visits, for instance. ... K-through-12 education. But still, at the end of the day, they are ineligible for every other government program you can name. Every piece of research on this shows that [undocumented workers] are paying far more than their fair share."

    They even help pay for the federal agents who raid their houses and scare their children.