Talking numbers...

Estimates of the total number of illegal immigrants are anywhere from 11 million to 20 million, depending on who you talk to about the issue.

Now, let's discuss some other numbers: 1,421,911 + 15,757 + 713,990 + 9,788 + 2,177 + 1,826 + 102,338 = 2,226,787

The math problem above is the total prison population in the United States, at least according to the latest DOJ estimates available.

In other words, the number of illegal immigrants is at least five times the size of our total prison population, and that is using the low-end figures. If you want to use the high-end of 20 million, it's nine times the size of our total prison population. And that is before we discuss one person who either gave an illegal immigrant a job, smuggled them across the border, or assisted them in any way (including not informing law enforcement they were here illegally).

The numbers don't lie. We have non-compliance with the law that is way beyond our prison capacity. There is no way to get them all, and what is worse, it's pretty clear to everyone who knows the numbers, and who can rationally look at them.

As BaseballCrank points out, there are reasons to provide an amnesty. The second reason he provides is as follows:

A second reason why amnesties are sometimes granted has nothing to do with justice, and everything to do with peace: sometimes, a society simply finds it easier to look the other way at certain past crimes than bring everyone guilty to justice. Countries like Chile and South Africa (and, less formally, East Germany) have taken this route at least to some extent after a change away from a repressive government, concluding that too many people were complicit to prosecute them all without expending massive resources on a backward-looking process and undergoing the wrenching process of tossing huge numbers of people in prison.

Certainly, fear of social disruption is why nearly all of even the most aggressive opponents of illegal immigration blanch at the notion of mass deportations of millions of people (including whole families and long-term residents), despite the fact that we have the perfect legal right to do just that. (The preferred solution is generally an 'attrition' strategy of gradually drying up the opportunities for illegal employment)

When the lawbreaking exceeds the prison population by a factor of at least five, things have passed the critical mass for social disruption by a very wide margin, particularly when it involves taking people into custody and detaining them. We are told by some that passing stricter laws and a greater deal of interior enforcement will lead illegal immigrants to deport themselves. It is a false promise - the underground economy and the informal economy are both out there, and neither of those things are going away outside outlawing cash transactions, barter, or other approaches (Who said payment had to be in dollars? It could be as simple as someone agreeing to clean bathrooms once a week in exchange for taking a family to eat dinner at McDonald's that day).

And when they don't self-deport, what then? That is the question they have to answer. If they're not going to do anything, then we're worse off than before, throwing good laws after bad, looking bad while doing so, and generating even more disrespect for the law than had we just let the status quo continue. Further measures to clamp down would be needed, but things would not stay static. More people would start to resist. People would come up with new means of faking documents. The inevitable result is more and more government intrusion into our lives - and that is not a good thing. This is what the "enforcement first" approach will lead to. A bifurcated process will never see the promised second part - the guest worker program/normalization - enacted, any more than the Simpson-Mazzoli approach delivered on enforcement. "Enforcement first" really means "enforcement only" when you look at it. If one side gets what it wants, they will have no incentive to cooperate on the second half of any process.

At this point, we need to set up some way of solving this problem. Mass deportation (including self-deportation) is a non-starter. What is needed is a large scale plea-bargain/pre-trial diversion that will collect some recompense for the violation of the law. This is NOT amnesty by the generally accepted definition (see the dictionary). There is punishment for violating the law - it will just not be the punishment demanded by the hard-liners and purists on this issue.

That is the reality of the situation. It needs to be dealt with on that basis, and not subjected to fear-mongering that has no more basis in truth than the claims that Republicans were cutting Medicare did in 1995. Conservatives have embraced tactics equivalent to Bill Clinton's Mediscare campaign in order to avoid facing a difficult problem facing this country and solving it. That is not good for the country - because it means the problem not only remains, but it festers that much longer, until reality becomes impossible to ignore. Then, solving the problem becomes that much harder.