it is a tough issue. it kinda goes against our philosophy and history to completely close the borders.
and, if you are really curious, then i suggest you follow the money trail. that usually points to the logic of the seemingly illogical.
I'm not advocating in cutting legal immigration, just stopping illegal immigration. We in Australia are very serious about stopping illegal immigration and actually what happened is that public support for immigration increased, not decreased. I feel for Americans as for Australians, they see the illegal immigration issue as a issue of people obeying the law, rather than we hate the Spics.