'Nation of Immigrants'
The pro-illegal side (which includes most of the Beltway Republicans) is fond of saying "We're a nation of immigrants!" as a final and definitive argument.
Well, let's take a look. First, every nation except possibly Ethiopia is composed of immigrants. The human species apparently started somewhere in East Africa and spread over the earth in an uncountable series of migrations. Certainly every country in the Western Hemisphere is a mix of early Siberian immigrants and fairly recent immigrants from Europe and elsewhere. So this phrase doesn't describe the United States in any unique way.
Second, there's nothing in the Constitution that requires open borders or forbids closing borders. Favoring lots of immigration was an important policy in the late 1800's because we had a huge empty territory in the West that needed to be settled. Later on, as the frontier became full, we gradually closed the inlet valve. If we're going to use cultural imperatives from 1850 as the basis of modern policy, we should also bring back slavery and industrial sweatshops, and take away women's vote.
"Give me your tired, your poor..." is a poem, not a law of nature, for heaven's sake. If we're going to use poems from that period as the basis of policy, let's go all the way!
Underneath all the jabber, there is exactly one important and valid reason to favor well-regulated
immigration: our mainly Protestant natives are reproducing below the replacement rate. Only the Catholics from Mexico are still having (and loving) new children. So we need to make it easy for them to settle here and assimilate. Current policy makes citizenship terribly difficult, and makes working illegally very easy. We need to reverse the reward/punishment pattern.