I do agree with your assessment and the plight of those trying to get in, and there are two points to be made here: one is the wall idea… could you imagine our building a wall on the border like the one around the Vatican that the Pope says is UnChristian? https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiy0paB5IvLAhWFox4KHeBOCT8QjRwIBw&url=http%3A%2F%2Fwww.washingtonstarnews.com%2Fthe-popes-giant-anti-christian-border-wall-around-vatican%2F&psig=AFQjCNFzII_DvqEQc0gKcK7oFgRcmx23hQ&ust=1456244561319309
The second though is to demographics: The bigger question is if we continuously let immigrants in the US it will directly affect the way our elections are run and how are government operates. For example, I live in SC which is a huge retirement location for people from the North. The come down here and think the we way run government should be more like the highly taxed north. So they get on our councils and legislatures and work hard to make South Carolina act like New York. The same goes for those believers of Sharia Law or the Hispanic community that want to create their own new nation state from Southern CA to Texas. While you say, oh they are too small in number to ever do that, when do you stop the flow. In 100 years when they do gain a majority?