Nationalism, Borders, and Migration: purpose?

Personally, I have nothing against people traveling, learning new languages, and living responsibly and participating in the economy wherever they go.

However, I wonder what people think the most important purpose of nations, borders, and (anti)migration are:

1) keeping the world segregated into transgenerationally stabilized national populations, with minimal migration between (national) regions.

2) limiting and controlling migration for the sake of controlling crime, drug/human trafficking, and other exploitative transnational activities.

Imo, it would be a bad idea to allow freeer transnational traffic because it would facilitate more/easier trafficking of drugs/sex and other exploitative economic commerce (legal and illegal).

Which do you think is a more important purpose for nation states and border control? Are you afraid of a world where people are free to move anywhere in the world and participate in the local economy where they go?

Further, do you think it is possible to eliminate bias and discrimination against national/ethnic others; and if not do you think it is good to create economic push/pull factors that drive people to migrate and thus become subjected to discrimination as being 'foreign?'