I see it as more of a "Rule of Law" issue. I agree that our current immigration system is screwed, and we should reform how we legally bring new folks into this country. But it IS the current system, and you don't get to just bypass laws you don't like. There's a TON of laws in the US right now, that are part of a screwed up system, that would make life better for my family and I to ignore. But we don't, because it's important that we live in a country where the laws mean something, and are applied equally to all.
So in addition to making a lower caste of citizens for the Dem's to exploit, ignoring illegal immigration, or worse granting it legitimacy, ala "Undocumented" wordplay, chips away at one of the bedrocks that keeps our nation stable, and allows us to live with such diverse cultures and pretty low levels of angst and violence.
Basically: People need to follow the Law, until they get it changed. Not disregard the parts they don't like.