You know the conventional wisdom about progressives: We are divided by single-issue politics and unable to articulate a set of core values. The left, the argument goes, needs to take a page from the playbook of conservatives, who are unified, disciplined and relentlessly "on message."

Simple enough? Sure. Except when it isn't true. On some issues, there is dissent in conservative ranks. And it's not just the worried cries of moderate Republicans concerned that voters will balk at the agenda of the radical right, but deep and genuine divisions in principle.

Immigration is a case in point. On one side of the fence are the nativist conservatives who raise the alarm about hordes of foreigners invading our nation. Since 9/11, national security has been their rallying cry for restrictions on immigration, but their fear of immigrants' alleged criminality, welfare dependency, "bad character" and refusal to assimilate go back much further.

On the other side are the pro-business conservatives who insist that our economy needs the cheap labor provided by illegal immigrants.

This matchup pits the U.S. Chamber of Commerce against the armed "Minute Men" patrolling the southern border.

Even the president is confused. At the very last minute, he took Homeland Security Secretary Chertoff and Labor Secretary Chao off of the witness list at Tuesday’s Senate Judiciary Committee hearings on immigration reform. As The Washington Post put it, “So divided is the administration that its leading members aren’t even allowed to talk about the subject in public.”

What's a conservative to do? Even more perplexingly, what's a conservative think tank to do?

While many think tanks on the right have taken a tepid stance on immigration and mostly seek to deemphasize the issue, the Manhattan Institute has a different approach: Have two senior fellows play opposite sides of the issue. Senior Fellow Heather MacDonald pens passionate editorials deploring how "the constant invasion of illegal aliens is worsening gang violence," and insisting that an "open-borders regime is folly," even as Senior Fellow Tamar Jacoby argues in favor of amnesty because America's economy depends on undocumented workers.

Heather MacDonald has a simple opinion about immigrants: They are bad, legal or illegal. The author of such articles as "The Immigrant Gang Plague" warns about the emerging "Latino Underclass"—a wave of immigrants predisposed to becoming gangbangers and drug dealers. "To be sure, most Hispanics are hardworking, law abiding residents," states Mac Donald, "yet given the magnitude of present immigration levels, if only a portion of those from south of the border goes bad, the costs to society will be enormous."

Citing a study from the Federal Reserve Bank of Dallas to the effect that "ethnicity matters" in education, MacDonald implies that Latinos are uneducable. "No one knows why this is so," continues MacDonald, who then cites as her sole source of evidence "an unwed Salvadoran welfare mother in Santa Ana," who states, "Hispanic parents are the kind of parents that leave it to others…we don't get that involved."

As a former member of a City University of New York task force, MacDonald should know that when Latinos are presented with the opportunity, they achieve academically. In fact, the number of Hispanics receiving college degrees has quadrupled since 1978. Mac Donald's view is hysterical considering the sacrifice that so many immigrant parents make precisely for their children's education.

Taking a wholly different view are pro-business conservatives who romanticize proposals to grant short-term amnesty to illegal immigrants so they can do jobs that American citizens won't. Tamar Jacoby argues, "Our increasingly educated, middle-class workforce isn't interested in hard manual work, but millions of campesinos south of the border are. We need them and they need us—supply and demand—and the resulting flow is good for our economy."

Yes, illegal immigrants perform important functions in our economy and always have. But Jacoby neglects the principle reason these jobs do not appeal to American citizens: They don’t pay wages that put food on the table. Instead of questioning the industry practices behind low wages—especially those that also put our "increasingly educated, middle-class workforce" at record risk of unemployment and career insecurity—Jacoby believes immigrant labor is the answer. If there is a demand for workers who won't mind being exploited, we should legalize the supply.

Of course, the Manhattan Institute inner conflict is only an emblem of the larger conflict between the policy shops of the right. The Heritage Foundation has offered its litmus test for any immigration bill, emphasizing “internal enforcement of immigration laws, the origins of illegal migration, and border security.” Cato argues the case that immigration is at a historic low, and that immigrants “create at least as many jobs as they fill.” So much for being on message.

The fissure on the right over immigration policy gives the left a golden opportunity. Now is the time to articulate a vision of how progressive immigration policy is in the best interest of our nation and its families. While many from both sides of the aisle are lining up behind the Secure America and Orderly Immigration Act sponsored by Sens. John McCain and Ted Kennedy, adopting a purely legislative strategy is short-sighted.

The issue of immigration divides America. Beyond support for a specific bill, we must offer a conceptual framework that unites the vast majority of Americans struggling to understand their connection to the American Dream. We should measure our ultimate success not by how many votes a bill gets on Capitol Hill, but how the narrative we offer resonates with voters from San Diego to Raleigh.

Executive Director of the Drum Major Institute for Public Policy