Why, ourselves, of course!
By 'the undocumented," of course, I'm referring to those folks normally referred to as "illegal." But, since it's impossible to pass a law against the existence of people, "undocumented" makes so much more sense. The undocumented are simply people who are here, but their papers aren't in order. And, if you had any idea of how costly and complicated it is to get one's papers in order, you would begin to understand how inevitable it is to have so many people who are here, but not under the full color of law.
Instead, so many of the people who are anti-undocumented based on racism or ignorance (if that's not repeating myself) defend their views in terms of public safety. Immigrants are a menace to our communities, and that justifies enormous public effort and expense to remove them from our midst.
But, leaving aside the fact that this view simply isn't true, statistically or otherwise, it is actually dangerous to not provide assistance to the undocumented. Like it or not, the undocumented have taken jobs native-born Americans will not do, raising families and building community roles in the process. They have become part of the social and economic fabric of America, while we have looked the other way, perhaps ashamed of the fact that all of us have played some role in their exploitation.
Looking the other way has a price tag, however. Here is at least part of that price tag. On the other hand, facing reality has real benefits. Here is an example.
We live in a world in which money moves around it at the speed of light, yet people can only move at the speed of sludge. We need comprehensive immigration reform--not just at the national level, but at the international level as well. Perhaps, if Americans faced fewer obstacles to travelling abroad, and enjoy more opportunity in the process, perhaps they will recognize more easily that, when they hurt the undocumented, they hurt themselves.