A lot of the justification for borders seem to me like the defence of apartheid gone global. Why is it moral to trap people iin poverty within an artificial creation like a nation-state for the various governments of the world to do as they wish to them
I mean on deontological grounds, closed borders are basically indefensible. People have a right to be free and own themselves (not held within the binds of a government they only have a part of).
So is there really a moral defence that says it is OK for governments to keep someone from migrating from Congo to Europe, but that it is immoral for the Soviet Union to stop Siberians moving to Moscow?
We all have different morals. It is not in my book.
Yes: everything is both defensible and indefensible, because we all have a different moral system. This is one of the key failures of modernity.
It's also relevant to the discussion at hand, because, with unrestricted immigration, a population is guaranteed to host conflicting moral views.