Fixing the "magic dirt" problem
Just the Basics
However, the emphasis has to be on keeping the numbers low. In America's case, given a population of about 330 million right now, this means less than 30,000 highly skilled immigrants (that's a growth rate of 0.01%) per year- and even that might be too many. That chart above shows that, as immigration has increased, native labour-force participation has decreased (which is to be expected).
This spells disaster for the United States, and any other nation that follows a similar pattern, if not checked and reversed.
Problem is, if you decide to let, say, Iranians into the country en masse along with Arabs, you're also going to be importing a religious feud that dates back some 12 centuries with them. You want American town and city streets to be slick with blood? Go right ahead with that, then.
The same is true for just about any other major ethnic group, race, or nationality that you care to name. All of them have blood feuds and prejudices and beefs with others. All of them will turn violent sooner or later.
Skin in the Game
Some Modest Proposals
6. No dual-citizenship
While we're on the subject of civic duty- let's have done with this silly practice of allowing people to retain citizenship of their original nations.
If you want to be an American, bloody well be an American. If you insist on retaining your passport from Thirdworldhellistan, just so that you can go back and visit family now and then, well, sorry, but you're just not American.
An American passport allows one to travel to most parts of the world without a visa. Those that do require visas for American citizens are generally fairly quick to give them- particularly pro-American parts of Europe and Asia, like Poland in the former and the Philippines in the latter. If you want the privileges that come with being an American citizen, then you should jolly well be prepared to put up with a few inconveniences along the way.
Moreover, being a citizen of another nation means that your allegiance to the American Republic, people, and way of life is deeply suspect. Let's not pretend otherwise- if you have loyalties of any kind to another nation, how exactly are Americans supposed to expect you to help them out in times of war and crisis?