Rather like "Brexit means Brexit", saying that things "are what they are" is basically meaningless (take note, Exodus). And anyway, human nature being what it is also allows for cooperation, on potentially huge scales too.
Thanks for the song lyrics, ellipsis.
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Now, to AOG. No, it's not valid at all. Firstly, the "borders" of my house don't extend very far; secondly, on a purely geographical issue, the question of who is welcome and how many people can physically stay in the place puts a limit on how open it can really be anyway; thirdly, literally right outside the door is something called a "street", where people from all "countries" are free to roam as they like, subject to some international laws (highway code) of course; in essence, I am comparing the hoped-for lack of borders to the situation *outside* the house.
I could add, too, that since I don't own the place I stay, the owner instead has done exactly what you are trying to imply people don't do. Subject to certain conditions, though, he has invited four strangers into a place he owns to use the resources and property that is his, as if it were their own.
Further, the concept of borders around a house is as much related to practical considerations such as shelter from the elements, long-term storage of food and personal resources, etc. Yes, and security too, there's no getting around that, but it's security of a very, very different nature. And, again, there's the problem of viewing the situation *now* as eternal, despite trends generally pointing in the other direction. Public perception being what it is, this rarely gets the attention it deserves, but it's true all the same.
Maybe there is a limit to how far the trends can go, and maybe it is, after all, far short of the future I hope for. Still, I guess what I'm mainly trying to say is that we have yet to reach that limit. After all, it would be fairly depressing to think that the world as it is today is as good as it gets, as united as humanity can be.