How do immigrants impact our economy? Are they draining our social services system? Destroying our middle class? Or are they the backbone of our economy, working in jobs that Americans don’t want, subsidizing our Social Security system and paying millions in taxes? Like most of the discussion around immigration, there are no easy answers, and, often, there seems to be no middle ground on this issue.

What of the charges that undocumented immigrants are free-riding ff the system? As we learned in economics recently, most research indicates that immigrants pay more in taxes than the services they consume. This, however, does not factor in the national military budget as a service consumed.

In addition, undocumented immigrants are shoring up our Social Security system, providing it with a subsidy of as much as $7 billion a year – benefits they will never reap upon retirement. That represented 10 percent of the budget surplus in 2004, the difference between what the system currently receives in payroll taxes and what it doles out in pension benefits.

Many undocumented immigrants also pay taxes using Individual Taxpayer Identification Numbers, which are issued by the Internal Revenue Service to people who can’t get Social Security numbers. When I wrote an article about this in 2003, the IRS had already issued more than 6.8 million of these numbers. About 366,000 returns were filed using individual taxpayer identification numbers in 2001, according to IRS data from that year. People with the tax numbers reported wages of almost $7 billion and paid almost $305 million in taxes, according to the IRS.

Why do they pay? One housepainter I interviewed said he wanted to show that immigrants contribute to the U.S. economy. He also wanted to establish a record that he paid taxes in the hopes that he might one day be able to apply for legalization.

While in Los Angeles, I heard a representative from the Federation for American Immigration Reform, a group that advocates reducing immigration, talking about how undocumented immigrants would destroy the middle class.

It was a puzzling statement, given another econ lecture, where we learned that immigration impacts natives in a net positive way. That’s not to say, however, that it affects everyone equally. Immigration “harms workers who are substitutes for immigrants while benefiting workers who are complements to immigrants. Most economists believe that unskilled domestic workers are the substitutes, so their wages will fall, and skilled domestic workers are complements, so their wages will rise,” James Smith and Barry Edmonston write in “The New Americans: Economic, Demographic, and Fiscal Effects of Immigration.” Smith and Edmonston estimate the domestic gain from immigration is from $1 to $10 billion a year. “This gain may be modest relative to the size of the U.S. economy, but it remains a significant positive gain in absolute terms,” they conclude. Additionally, everyone – including low-skilled workers – benefits from the lower prices of consumer goods produced by immigrant labor.

Harvard University economist George Borjas has posited that many native workers at the bottom of the skill level have much to fear from the entry of less-skilled immigrants. Immigrants “take jobs that natives do not want at the going wage,” he notes in “Heaven’s Door: Immigration Policy and the American Economy.” “In other words, it might be the case that natives might not want to work in some of the jobs that immigrants have. This does not say, however, that natives would refuse to work in those jobs if the immigrants had never arrived and employers were forced to raise wages to fill those positions.”

The issue becomes even more contentious when race is introduced. "In this era of mass immigration, no group has benefited less or been harmed more than the African American population," Vernon M. Briggs Jr., a Cornell University labor economist who has studied the effect of immigration on blacks for more than three decades, told the LA Times recently.

In a 2004 book, "The Impact of Immigration on African Americans," Briggs and other scholars found immigration resulted in lower wages for less skilled and less educated blacks. They also found it displaced blacks from the job market, and resulted in many dropping out of the labor pool entirely, the LA Times reports. However, the Times article does not note whether the scholars considered other factors, such as discrimination, work experience and educational attainment, as determinants of the outcomes they list.

The scholars also found some positive effects: larger numbers of low-skilled workers helped push better-educated blacks up the occupational ladder, enhancing their managerial opportunities, the LA Times notes.

Maria Elena Durazo, the Los Angeles County Federation of Labor's interim executive secretary-treasurer, told the LA Times the solution was to demand that employers actively recruit and train more blacks. "Hiring immigrants was one way in which wages and benefits could be held down," Durazo said. "Now immigrants are proud of making these jobs better jobs, and we believe that African Americans have to be given opportunities."

Recent op-ed pieces in the New York Times suggest the U.S. would be better served if it reshapes its immigration policy to attract skilled immigrants rather than low-skilled ones. “The broader problem is that our immigration program is structured so as to bring in cheap laborers more than brilliant minds,” notes New York Times columnist Nicholas Kristof. “So let's go ahead and regularize longtime illegals, rather than leaving them forever in the shadows. But instead of bringing in a new flood of guest workers, let's recast our generosity more toward biologists and computer programmers.” I don’t think this is the entire solution. While Kristof has a point, I think the answer lies in a balance between low- and high-skilled workers. If we encourage only high-skilled workers, this results in an elitist and one-sided immigration policy.

At the most basic level, undocumented immigrants are the people who keep our economy running. They pick the produce we buy in supermarkets, slaughter the chicken on our dinner plates, make our hotel beds, take care of our children, mow our lawns, build our homes and cook meals at our favorite restaurants. As we evolve into a more service-oriented economy, the demand for these workers will be even greater. For example, fluffy new beds being touted by hotel chains require housekeepers to wrestle with an array of pillows, duvet covers, down comforters, 300-thread-count sheets, shams, bed skirts, bolsters and bed scarves – resulting in increased injury rates for workers, many of whom are immigrants and women.

And at a time when some native workers turn up their noses at even fast food jobs, I don’t think many would be clamoring for the job that killed Jose Alatorre. A welder at a dairy plant in the Central Valley, Alatorre drowned in liquid cow manure while trying to repair a clogged pump that channeled cow waste.

Would our economy come to a grinding halt without the labor of undocumented immigrants? Maybe we’ll find out. Two men who helped organize the massive protests in downtown Los Angeles told the LA Times that their next major action will be to call a boycott of work, school and consumer activities on May 1.

NEXT: Building a movement: Can advocates sustain the passion and energy that’s propelled hundreds of thousands into the streets to protest immigration reform?