Boarders, including ours, use to be boundaries containing a “common” culture which allows for a government to function properly. If you have no boarders and you create a mix of cultures then it become impossible to govern — unless you have a powerful central government and a police state, and even then it is very very hard. This principle is a first principle of government and when violated will led to the destruction of the country that tries it. And that kind reader is what “Open” borders is all about