Since I live in California, I wanted to offer a few random thoughts about the whole immigration law contretemps. I'm not driving toward a particular conclusion here. I just want to offer some fodder for discussion.
California's economy is deeply dependent on the labor of undocumented workers. This is true in agribusiness, obviously, but it's also true in a number of other sectors, including restaurants, certain types of construction, janitorial services, personal care services (e.g. nannies, elder care, home cleaning services, etc.). Californians like to wax indignant about undocumented workers, but they often don't see the connection between their relatively comfortable standard of living and the large pool of undocumented laborers that supports it.
There is no question that the continued influx of undocumented workers has a labor market impact. There is certainly literature on this. As an anecdote, I'll offer that decades ago the Service Employees International Union had a master contract covering janitorial contractors in Los Angeles. The vast majority of those janitors were African-American. In the late 70s/early 80s, non-union contractors employing immigrant workers (both documented and undocumented) began to underbid contractors particpating in the master agreement. It took SEIU another decade to reorganize the industry, which is now almost entirely Latino.
The influx of both legal and illegal immigrants also has had a major impact on public services in California, particularly in education and health care. One-third of the population of Los Angeles County has no health insurance, which is at least one of the reasons (not the only one) that the county hospital system is in a perpetual state of crisis. However, what is not generally realized is that many illegal immigrants are, in fact, paying taxes: sales, property and even income taxes in some cases.
Having said all this, I'm not sure I see a solution. A cursory glance at human history suggests that borders on a map have never really prevented people who really wanted to migrate from doing so. A nation certainly has a right to police its borders, and enforcement activity can help reduce the number of illegal border crossings. But there is also a real limit to what border enforcement can accomplish. A significant number of illegal immigrants are people who overstay temporary visas. The border economies are deeply intertwined, with thousands of people crossing each day to work, shop and socialize. Families are often composed of individuals who are legally here and those that aren't.
As to the legislation passed by the House last fall that has come under criticism by a number of Bishops, I haven't read it yet, so I won't offer my opinions. But I will say that those who believe that vaguely worded laws don't invite abuse of prosecutorial discretion are being a bit nave. But I don't know enough yet to say whether that is the case here.