With any issue in current events, there are always lots of theories being cast about, but not too much data. Once again, I've gotta give credit to the Center for Urban Economic Development at my college; its research about the positive economic impacts of immigrants plays those Minutemen for chumps.
Just a year ago, Republicans made a huge deal about Social Security--who will be around to work and pay taxes when the Baby Boomers retire? Oh no! Now, they want to evict 10+ million relatively young workers and families that pay payroll, sales, and property taxes. Brilliant. Since the data isn't on their side, I believe that the real issue for conservatives, as always, is the fear of people who are different. Different languages, different food, different customs.
Get over it people. This is a big country. There's room for everybody. Now lets set up a program so we can let as many people come in as we need, give anyone a chance to earn citizenship, and make sure that anyone who is here has ID. Done.