Ingroup/outgroup dynamics are a pretty deeply-rooted aspect of human social behavior. Maybe it doesn't always manifest itself in the form of a Westphalian nation-state, but it does point to something deep inside us that we manifest at various levels.

This sort of tactical nihilism is honestly pretty confusing to me. Borders, whether national, ideological, social, tribal, linguistic, etc. always have some level of arbitrariness to them, and yet they still represent useful categories. The house door that you lock every evening is merely a collection of arbitrary atoms arranged to separate what you imagine to be your property from others. In the framework of nations, the idea of treating citizens differently from non-citizens as being "discrimination" is an odd one. A country belongs to its people; it doesn't belong to those across the arbitrary border. We all make (sometimes arbitrary) restrictions on access to that which we value; humans who don't do that usually end up losing them to those who do.

I haven't seen anyone in this thread argue for dissolving borders or having a single world government (although a few people have been arguing vehemently against it). It's perfectly reasonable to support national borders with strong checks for safety, while still supporting an extremely welcoming immigrant worker policy.

It is, but now we know better.