I am sure other countries would not allow America to do this. Specially European countries.
What are you smoking? There's a pretty large swell of anti-immigrant sentiment on the rise in Europe right now. Particularly directed at Muslim immigrants.
British, Swiss, Dutch, Germans, and the French even are all getting sick of the problems caused by excessive amounts of immigrants who DON'T ASSIMILATE.
There is a reason Mexico is a terrible country--it's full of Mexicans with Mexican culture. There's a reason America is a great country--It's full of Americans with American culture, which of course is heavily derived from Britain. Virtually every place Britain touched is a powerhouse in their region--USA, Canada, Australia, South Africa, Hong Kong, Singapore, the list goes on. All the politically correct retards preaching "diversity" and crying about "ethno-centrism" need to get a strong dose of reality--certain cultures are vastly superior to others, and it's clearly demonstrated across the world.
Immigrants used to want to come here and be part of our extremely prosperous culture and become AMERICANS, the Mexicans just want to turn it into Mexico. They're Mexicans first, Americans second, the last thing the US needs right now is a 5th column 20 million strong.