I'm not really sure what our immigration policy priorities are, let alone what they should be. There is some viscious and biased information about how immigrants impact our economy and our society, and at times it makes me sick, as most of it is motivated by little more than prejudice and Nationalism (read: not simply "Patriotism"). But immigration is problematic: Although the free flow of migrant labor does generally help the "average" citizen certain pockets of the native workforce would be hurt. Furthermore, there is some argument to be made that policies should include some allowances to help those unfortunate souls who have been born into poverty around the world (so long as they can demonstrate some ability to be productive in our economy).
One of the most unfortunate facts about immigrants is that they tend to be less educated than US natives. There is no disputing this. Some would go so far as to say that they are "the stupidest of their own populations," as Benjamin Franklin did about German immigrants over 200 years ago. Some would go yet another step and advocate policies that ensure that those who are allowed to immigrate here are only those who are the most highly-educated and skilled. That may artificially increase our workforce education levels, but is it even desirable? Gains from trade primarily come from the fact that countries are different, and if immigration is a potential source of reaping these gains and we are a relatively skill-abundant workforce, the argument could be made that the greatest gains would come from allowing the entry of less-skilled immigrants, not more-skilled.
Another problem I have with pundits who cite these differences in education between natives and immigrants is that we have a long tradition for forming our immigration policies in a way that helps the least fortunate abroad, and we recognize that there are countries in which the poor and displaced have a much harder time of things than they would here. One fact that I could cite here is that refugees are consistently measured to be the least skilled of all legal immigrants to the US. Does that mean we should eliminate refugee status as a visa class preference? Few would argue for that.
So the problem is this: for immigration policy to work it should do let's say four things. First, it should do something to stem the tide of undocumented aliens who enter as a matter of national security. No amount of restriction and no practical amount of spending on enforcement will stop people from trying to enter. The question is more one of managing it optimally and minimizing the externalities of the undocumented entry (such as smuggling of drugs and weapons or the threat of terrorism) rather than trying to exclude anything beyond the arbitrarily-defined quota. Second, policy should be motivated by our national economic interests, and here I specifially mean aggregate welfare. Unskilled labor may contribute most to aggregate welfare on a per capita basis. However, it will have serious consequences for certain groups, and these do tend to be those with the most modest means in our society. So, the third and fourth parts of our policy (and the most complicated) is concern for those less fortunate, but would include: (1) natives, and; (2) those living in adverse conditions around the world. Poverty in our own country is a problem, and increases in immigration would have serious adverse impacts for natives who lack at least a high school education. However this "foreignization of poverty" is not something I worry much about because the "foreign poverty" that immigration brings represents immigrants who are moving from one form of poverty to a "better" level of poverty. Yet, two-thirds of the world is living in a "Less-Developed" Country, as defined by the World Bank. Many of these countries lack the institutional stability and transparency in governance that would allow entrepreneurial talent to flourish, or even allocate resources to those well-suited to use them profitably.
So these are my priorities. The only one of them that would not be well-served by having a more open border is number three, concern for the native poor. Since I don't want to trivialize this concern, I am open to suggestions for how the main objectives (namely numbers 1 and 2) could be achieved.