Why do you say so? There's nothing inherently "good" or "just" about nation states. The only nominal support I can find for such an idea is rooted in applying something like Dunbar's Number[1]. But arguably appealing to that is committing a variation of the naturalistic fallacy[2].
The ridiculous treatment of the individual in the situation is something we should come down hard on that section of the government. (They should be facing an inquiry about that)
But who's going to conduct such an inquiry? The government? Oh, wait. It's the old "who watches the watchers?" problem. Me, I don't trust the government to provide oversight of itself. For the same reason I don't trust police to police themselves when it comes to excessive force cases, etc.
Without borders or nations, you're suggesting there will be a universal law. Who's law do you want? Do you want to be forced to wear head coverings, do you want internet censorship? Do you want to have kickbacks from the cartel? Having different nations allows you to understand where there are tradeoffs.
Can you back up that assertion?
The border between the US and Mexico exists because the US and Mexico have different laws (including taxation and benefits). The border is where the US and Mexico have negotiated that one's rules stop holding and the other's rules start holding.
For taxes and things, sure. For oppression of peoples? Probably. To keep undesirable countries citizens out? Sure. To have an excuse not to care about what goes on in other countries? Most definitely.
Travel and freedom of movement and work and choice in where you wind up living? Not really.
The ridiculous treatment of the individual in the situation is something we should come down hard on that section of the government. (They should be facing an inquiry about that)