lines in the sand

In  "The Case for Getting Rid of Borders—Completely" at The Atlantic, Alex Tabarrok writes:

What moral theory justifies using wire, wall, and weapon to prevent people from moving to opportunity? ...No standard moral framework, be it utilitarian, libertarian, egalitarian, Rawlsian, Christian, or any other well-developed perspective, regards people from foreign lands as less entitled to exercise their rights—or as inherently possessing less moral worth—than people lucky to have been born in the right place at the right time.

Just imagine: no borders. Isn't that what John Lennon did, years ago?

Imagine there's no countries 
It isn't hard to do 
Nothing to kill or die for 
And no religion too 
Imagine all the people living life in peace