Unfortunately, they no longer do this. The "white" discovery of technology has meant more people needed for industrialized nations to function, and given the declining birth rates of more intelligent people, it has opened the flood gates for immigration. The thing I hate the most, people migrating in order to find a better life for "themselves," while not giving a damn about the consequences. I know this site/organization are strongly against that as well, but it is time governments woke up to the menace. I am South American, yet I hate it when I visit the US and see all the Mexican immigrants/spawn of overpopulation who think they're invincible and act like f-in retards. Most of em seem to be doing minimum or low wage jobs, getting an obese Mexican wife, and reproducing in droves, with stupid kids fooling around. Maybe Mexico once owned the South, etc. etc., but I think there's a difference between coming to make a culture great and just coming to usurp the best out of it. If they had any reasonable intelligence, these people (or their ancestors) would have stayed back and tried to make something great out of it (and stopped having so many kids as well).
At the other end are the Chinese and their variants, who seem to be taking over the world. I am not racist, and do have many Mexican and Chinese friends, yet I have told some of them this face to face (while expecting them to be critical of Brazilia which is another f-in mess). Yet most seem to be unable to see the big picture.
Oh dear, it appears I am strongly for eugenics 
I completely understand your sentiment.
The biggest culprits in all this are the governments from the countries these immigrants are coming from.
What is the take of these countries when they see their people leaving for the U.S? They are ecstatic. They get rid of more people they don't want, and those people, in turn, bring that money back into their home countries and into the overpaid government pockets.
In the grand scheme of things, no one really wins. The U.S. receives more people that it doesn't need, or those people who left for the U.S are forced to abandon their country and either not adapt with this new country or live amongst their own kind and essentially live in their own country. All while the countries that they left are cleansed of any responsibility, and things remain the same.
You know what would fix many of these issues? If the governments of the Mexican, or Guatemalan, or any of these countries who export tons of people gave a shit about their own people and decided to have some pride in their countries by working hard to fix it. Along with this, if the U.S. enforced a VERY STRICT policy against immigration, meaning, NO ONE ENTERS THE COUNTRY, maybe then, the Spanish elite run governments wouldn't have an excuse to not do anything about the shit piling up on their doorstep.