The opponents of immigration reform have many small complaints, but they really have one core concern. It’s about control. America doesn’t control its borders. Past reform efforts have not established control. Current proposals wouldn’t establish effective control.

But the opponents rarely say what exactly it is they are trying to control. They talk about border security and various mechanisms to achieve that, but they rarely go into detail about what we should be so vigilant about restricting. I thought I would spell it out.

First, immigration opponents are effectively trying to restrict the flow of conservatives into this country. In survey after survey, immigrants are found to have more traditional ideas about family structure and community than comparable Americans. They have lower incarceration rates. They place higher emphasis on career success. They have stronger work ethics. Immigrants go into poor neighborhoods and infuse them with traditional values.

When immigrant areas go bad, it’s not because they have infected America with bad values. It’s because America has infected them with bad values already present. So the first thing conservative opponents of reform are trying to restrict is social conservatism.

Second, immigration opponents are trying to restrict assimilation. The evidence about this is clear, too. Current immigrants enter this country because they want to realize the same dreams that inspired past waves. Study after study shows current Hispanic immigrants are picking up English at an impressive clip, roughly as quickly as earlier immigrant groups. They are making steady gains in homeownership rates, job status and social identity. By second generation, according to a Pew Research Center study released earlier this year, 61 percent of immigrants think of themselves as “typical Americans.”Third, immigration opponents are trying to restrict love affairs. Far from segregating themselves into their own alien subculture, today’s immigrant groups seem eager to marry into mainstream American society. Among all newlyweds in 2010, 9 percent of whites married outside of their racial or ethnic group, as did 17 percent of blacks. But an astonishing 26 percent of Hispanics and 28 percent of Asians married outside their groups. They are blending into America in the most intimate way.

Fourth, immigration opponents are trying to restrict social mobility. Generation after generation, the children of immigrants are gradually better educated and more affluent than their parents.

A few years ago, the great political scientist Samuel Huntington asserted that Hispanic immigrants were not succeeding as previous immigrants had. James P. Smith of the RAND Corporation conducted the most prominent investigation into this claim and concluded: “The concern that educational generational progress among Latino immigrants has lagged behind other immigrant groups is largely unfounded.”Some intelligent skeptics say that mobility is fine through the second generation but stalls by the third. It is indeed harder to rise in a more chaotic and fragmented society. But one of the country’s leading immigration researchers, Richard Alba of the City University of New York, calls the third generation stall “a statistical illusion.”Much of the research that shows the effect compares today’s third-generation immigrants with today’s second-generation group. But the third-generation families originally came to the U.S. decades ago, at a time when segregation was prevalent, discrimination was high and immigrants were harshly treated. You’d expect those families to progress more slowly than families that came to more welcoming conditions a generation later.

Fifth, immigration opponents are trying to restrict skills. Current reform proposals would increase high-skill immigration. Opponents of reform are trying to restrict an infusion of people most likely to start businesses and invent things.

Alba points out that, over the next decades, the retirement of the baby-boomer generation will open up a large number of positions, especially atop the labor force. He points out that the fastest-growing ethnic groups are already rising to fill these slots. Whites occupy 80 percent of the top-paying jobs among older workers. But, among younger workers, whites occupy only 67 percent of the top jobs. The work force is already more diverse the younger you go.

Finally, opponents of reform are trying to hold back the inevitable. Whether immigration reform passes or not, the United States is going to become a much more cosmopolitan country than it is now. The country will look more like the faces you see at college commencement exercises and less like the faces you see in senior citizen homes.

One crucial question is whether America will be better off in that future with today’s dysfunctional immigration laws or something else? Another interesting question is whether a major political party is going to consign itself to permanent irrelevance. If conservatives defeat immigration reform, the Republicans will definitely lose control of one thing for years to come: political power.