Selfish answer here because it's kicking the can down the road, but immigration is the best way to ensure that social spending programs don't go bankrupt due to demographic shifts toward older populations with fewer children. We have more than enough land in America to support people, immigrants help ensure the economic vitality of our country, immigrants tend to have a strong work ethic and, personally, really impress me -- it's a BOLD move to leave one country for permanent settlement in another, takes a lot of guts and a real vision to make life better for yourself and your family. Immigrants historically and in modern times bolster the cultural health of our country as well.
America is in a unique position in the developed world. For Europe, immigration has resulted in increased ethnic tensions and social unrest/unease. Europe also doesn't have the space to support immigration. But America? We have the historical foundations for successful immigration: we're a diverse country, with lots of economic opportunity. It's a blessing to be able to welcome greater numbers of immigrants to our country.
There are problems in the current system, because we aren't adequately equipped to handle all the demand to integrate. I'm not enough of an expert on the immigration system to recommend concrete solutions, but I think the general direction is overwhelmingly clear: immigration is good, and we should seek to make it easier to immigrate. I fully support a "back of the line" policy, where illegal immigrants are not deported but are allowed to stay in the country and placed behind legal immigrants in the queue to attain citizenship, in combination with devoting more resources to make the bureaucratic aspect of immigration more streamlined and efficient.