What is it good for?
Contrary to popular belief, the purpose of immigration laws isn't population control. It's white supremacist social engineering.
If it were truly about population control, it'd be completely indiscriminate. “The United States can only accept 29.4 million immigrants this year”—it’d be a sliding number, based on birth rate, death rate, and how effectively we can absorb that population—“and the requirements are you can't be a felon, need to get by in English, and need to get a job and residence within the first month.” And other reasonable things. Special accommodations for special cases, like refugees. Stuff absolutely anyone can do—again, special accommodations for special cases, like elderly parents immigrating with their kids, who are too senile to learn English or too disabled to work. But otherwise: Indiscriminate.
Thing is, the United States has always discriminated. Because our white supremacists don't want America to turn brown. They want it to remain a predominantly white, predominantly Protestant, country. Immigration mustn’t let in so many people that white Protestants become a minority; in fact, wherever possible, they hope to tip the scale further in their direction. Pity so many of the white Protestants in the world are perfectly happy staying in their homelands… although the white supremacists were able to get ahold of some white South Africans recently.