Some people who appreciate the US the most are those who have lived in other countries and societies.

As a student of history and economics, immigration has always been a controversial subject going back to our earliest days (Ben Franklin was against German immigrants, and the Dutch in NY were anti English). Immigration is what makes the US unique as a melting pot. From an economic perspective, we have had professors at UVa that studied the subject extensively. From a purely economic lens (not a global social equity perspective), immigration can be a huge positive if intelligently managed (but can also be a negative). And unfortunately, there have always been those on both sides who used immigration for political or partisan reasons to divide us, stoke fears, or gain advantage.