A ridiculous premise pushed by libertarians.
I understand that the true libertarian view is that when you have a libertarian society, you don’t need the borders. Until then, of course, you do.
Libertarian society? Do you mean globally? If we are the only country with open borders, how can that be beneficial to us as a nation? Or are we no longer a nation with borders and sovereignty?
From the 2012 Libertarian Party Platform
We support the removal of governmental impediments to free trade. Political freedom and escape from tyranny demand that individuals not be unreasonably constrained by government in the crossing of political boundaries. Economic freedom demands the unrestricted movement of human as well as financial capital across national borders. However, we support control over the entry into our country of foreign nationals who pose a credible threat to security, health or property.
Open borders is the libertarian philosophy, and it has always been their position.
See post 19.