What does open mean? What does respect private property mean? These are fundamental issues that not all cultures agree on, hence the borders. It's reasonable to at least know who is coming into a country if one wants to maintain values like property rights. Economics doesn't solve everything. But I do think politics/government and economics should be totally separate.

Anyone who isn't a known criminal or threat who wants to assimilate and provide for themselves should absolutely be free to enter the US.