It’s not about race per se. if people have similar values then race is unimportant
And that is the crux of the issue.
Since the vast majority of immigration these days is from south of the border...do those migrants share the same values as we do? Some would say yes. But if that were the case, why then aren't their home countries much...much more like the United States?
The fact that they aren't show's that the current set of migrants do not have a majority of the same values.
Furthermore, language and culture need to be taken into account. Is it better, or worse, for the continuity of a country to have more people speaking & reading in different languages, or is it better if they speak and read a common language?
Part of the reason why this country is fracturing more and more by the day is due to the increasing differences between not only the native citizens, but with those millions who migrate here annually both legally and illegally.
What holds a country together best is a common language, a common culture, a common history and of course defined and secured borders.