One of the problems with any kind of omnibus bill is that supporters will argue the whole bill must be passed based on the claimed merits of specific pieces. This was the whole purpose of the DREAM Act: Advocates pointed to the most sympathetic group of illegal aliens — those who came here as children and did well in school — as an unrebuttable argument for amnestying all 12 million illegals.
Likewise with the religious hierarchs' argument about amnesty more generally. The Catholic bishops and the National Association of Evangelicals argue that the claimed moral imperative for legalizing illegal aliens necessitates passage of a comprehensive bill that also doubles both legal immigration and guest-worker admissions. In effect, these men of the cloth have put themselves in the position of claiming that Congress is morally required to procure cheap, controllable labor for farmers and restaurant owners.
A Washington Post editorial Sunday tried something similar in examining the political impact of the Schumer-Rubio bill, S.744. Both the online headline ("Immigration's electoral effect shouldn't scare the GOP") and the dead-tree headlines ("The ballot bogeyman / Immigration reform would have little effect on election results, new research shows") traffic in part-vs.-whole sleight of hand. The "new research" in question is a May paper by Carson Bruno of the Hoover Institution. Bruno examined the likely impact on the 2012 presidential election if the illegal population had been legalized and qualified for citizenship by Election Day under the terms of Schumer-Rubio. He played out various scenarios with different assumptions regarding citizenship and turnout rates and concluded that "On the whole, the electoral effects are small and a weak excuse for Republicans to oppose comprehensive immigration reform with a pathway to citizenship."
From this the Post falsely claims that "Immigration reform would have little effect on election results." I say "falsely" because the amnesty itself accounts for only a small part of the long-term political impact of "immigration reform." Far more consequential is the fact that Schumer-Rubio doubles legal immigration from about 1 million a year to 2 million. (And that's not considering the post-amnesty baby boom likely among the legalized population; the Public Policy Institute of California found in that state that "Between 1987 and 1991, total fertility rates for foreign-born Hispanics increased from 3.2 to 4.4″, in large part because of the 1986 amnesty.)
My colleague Steven Camarota has calculated that some two-thirds of the potential new voters directly added by Schumer-Rubio would come as a result of the legal immigration increases, not the amnesty. Even prior to that, current immigration law is a Democratic-voter machine. Camarota concludes that "even without the effects of S.744, the current level of immigration will add 5.1 million new potential voting-age citizens to the country by 2024, 8.4 million by 2028, and 14.9 million by 2036." When you add the Senate bill's amnesty and legal-immigration increases, the total impact is much greater: "nearly 10 million potential voting-age citizens by 2024, and more than 32 million by 2036."
This part-vs.-whole problem is particularly acute with regard to the huge legal immigration increases in Schumer-Rubio. None of the arguments about "not splitting families" and "bringing people out of the shadows" is at all relevant to the issue of doubling future immigration of people who aren't here yet. You might think those increases are a good idea because today's 1 million legal immigrants a year isn't enough; but they're only included in the "comprehensive" bill because that's the only way to get corporate muscle and money to push for the amnesty as well.
This is why the House approach of targeted, subject-specific immigration bills is the only defensible approach. If you think amnesty is a good idea, argue for that — on its own. If you also think Congress has a responsibility to procure additional cheap labor for its billionaire benefactors, then make your case for that — separately. But mixing these two issues muddles the debate.