Opponents of comprehensive immigration reform argue that legalization rewards bad behavior.

Opponents of comprehensive immigration reform argue that legalization rewards bad behavior. They contend that illegal immigration is a crime that merits punishment and expulsion, not amnesty. The logic is that if we respond with tough enforcement, illegal immigrants will finally get that they aren't welcome here and go back to their home countries. This kind of reasoning is what's behind laws like the one recently passed in Arizona, which requires law enforcement personnel to determine whenever possible the immigration status of suspected illegal immigrants.

But immigrants aren't going home. We know this from experience. Despite high-profile raids, beefed-up border enforcement and the worst economy since the Depression, the size of the illegal immigrant population has declined by only a small fraction. At this pace, the time it would take to realize the pipe dream of removing illegal immigrants through forced and voluntary deportations could be measured in light-years.

Given that immigrants are here to stay, it is in everyone's interest for them to assimilate — to learn English, embrace U.S. social and civic customs and become part of the economic fabric. And if that is the goal, we need to have immigration reform that goes beyond fences, high-tech surveillance, more Border Patrol officers and a guest worker program. We need a path to legalization for those who have built lives here.

Why? Because illegal status inhibits not only the assimilation of those who are here illegally but of future generations who are U.S.-born citizens. Research has consistently found that illegal immigrants and their descendants have a much tougher time gaining a social and economic foothold.

On the other hand, we know that legalization has a positive effect on assimilation. The legalization program contained in the last major immigration overhaul, the 1986 Immigration Reform and Control Act, facilitated the assimilation of millions of immigrants and their children. A 2007 Merage Foundation report written by UC Irvine sociologists shows that the children of formerly illegal immigrants who obtain green cards face a brighter future and stand to contribute much more than those whose parents remain undocumented.

According to the study, U.S.-born Mexican-Americans whose fathers came illegally but later obtained legal permanent residency were 25 percent less likely to drop out of high school, 70 percent more likely to graduate from college, 13 percent more likely to prefer English at home, and their earnings were 30 percent higher than those whose fathers were illegal at the time of the survey.

Part of what holds the children of illegal immigrants back is that they can never quite look forward. Parents cannot fully participate in their children's lives in ways that help them realize their full potential. As children enter adulthood, many have to take care of the financial needs of their immigrant parents, whose illegal status makes them extremely vulnerable to the vagaries of the job market, the healthcare system and housing. The situation is worse for those who were brought as young children to the United States without documentation. They suffer from the double penalty of their parents' and their own illegality.

As Congress drags its feet on immigration reform, illegal immigrants continue to put down roots and the ranks of children who suffer the penalties of their parents illegal status swells. According to a recent Pew Hispanic Center report, almost half of all illegal immigrant households are couples with children, and the overwhelming majority of the children — 73 percent — are U.S. citizens. The number of U.S.-born children with at least one illegal immigrant parent grew to 4 million in 2008 from 2.7 million in 2003, a 48 percent increase. An additional 1.5 million children with at least one illegal immigrant parent are themselves illegal.

Withholding legalization imposes slow social and economic death on illegal immigrants and their children. Failure to implement comprehensive immigration reform leaves thousands of people who consider the United States their home in the shadows. It also deprives us of the opportunity to develop a better-trained workforce and to realize all the benefits, both social and economic, that a fully assimilated immigrant population can contribute. Legalization is the most crucial component of what Americans need and what they deserve: comprehensive immigration reform.

Tomas R. Jimenez is an assistant professor of sociology at Stanford University and an Irvine Fellow at the New America Foundation. He is the author of "Replenished Ethnicity: Mexican Americans, Immigration, and Identity." He wrote this for the Los Angeles Times.