I won't repeat all that I wrote in my defense of open immigration, but I will summarize by saying that the right to associate with whom you want, to own and live on the property you choose, to negotiate with whomever you please to sell your labor, are all rights that we have as humans, not via the state. These rights in effect pre-date, rather than flow from, the state, and as such should not be subject to citizenship test.
Anyway, Prawflawblog has a nice defense of immigration up as well:
Apparently both parties, with Republicans in the
lead, have embarked on an anti-immigrant frenzy. The hysteria has been
fueled for some time now by daily broadcasts in all major networks and
gravely sounding members of Congress discussing the "crisis on our
borders", "our bankrupt immigration system", etc. The virulence of this
sentiment makes Le Pen in France seem like a cosmopolitan liberal.
Yet liberal principles require a drastic reduction
of immigration controls. Foreigners flock to our shores because there
is demand for their labor. The same principle that supports free trade
of goods and services -- the law of comparative advantages -- applies
with equal force to freedom of movement. Freer immigration would
alleviate world poverty and allow people in our country to redirect
resources toward more efficient activities. Every single argument for
strict immigration controls is flawed
By the way, I know that "Social Security Reform" has been dropped from the media radar screen, even if the demographic problem hasn't gone away. If one is not willing to privatize it (as it should be) the next best alternative to the Social Security's demographic bomb is... allow free immigration. Nothing would do more to help the long-term Social Security picture like a few million new young immigrants hungry to work and perhaps to share in the American entrepreneurial spirit, paying their taxes to support the rest of us in our old age.