Strict immigration control is a relatively modern phenomenon, and you should reevaluate your viewpoint if you find it so easy to justify putting children in cages. Scratch that, justify other people putting children in cages. Most people who support these policies wouldn't have the stomach to do the dirty work themselves.
The present state of migration is also a modern phenomenon - otherwise, countries wouldn't be trending from more towards less homogeneous, but would already be in a 'steady state'.
Not true. People have been migrating from place to place for all of recorded history. Cultural homogeneity is nothing more than a "good ole days" fallacy; it's never really been a thing anywhere, except in the most remote parts of the world.
Look at the "Population by country of birth 1900-2016" graph for Sweden [1]. It is at ~100% in 1900, and ~82% in 2016.
The US went from 87.9% white in 1900, to 72.4% in 2010 [2]. Unfortunately, I couldn't find such demographic histories for other countries. But search for "US/Europe becoming more diverse", and you'll find countless articles, from mainstream publications, asserting this. So to claim otherwise is extremely fringe.
And there is mathematically no way for a place to be becoming more diverse, while keeping historically constant migration. If the migration hadn't changed in some way, then it would already be diverse. It also means that, if it's becoming more diverse, that it was less diverse, i.e. more homogeneous, in the past.
Looking at the present, China is 91.6% ethnically Han [3], and Hungary is 93.5% ethnically Hungarian [4]. So unless you think China or Hungary or US in 1900-1970 are "the most remote parts of the world", then no, homogeneity is provably not a fallacy.
So yes, "People have been migrating from place to place for all of recorded history", but both the rate and nature of this migration changed, and just a quick glance at the headlines of virtually any news source is enough to tell you this.
So your thesis is ~100 years ago was some freak historical period when countries were mostly homogeneous (compared to current day. Please don't cite e.g. Czechs and Slovaks living in the same country as diversity comparable to current day), but throughout the rest of history, diversity was much greater.
Do you have sources to back this up? And how did those countries become homogeneous, then?
How do you think all those European Americans got there?
And, modern nation states are very new. For example, France drove to extinction or near extinction all languages besides French spoken in what is now present day France through government policy. Like the language of Bretagne.
Your profound misunderstanding of history is not something I can rectify with citations. Read a book? Like, a scholarly book.
