Here’s a thought experiment.
If 150 million Bangladeshis vote with their feet to come to America, the "international apartheid" thesis says we are morally obligated to let them in. The American people don’t get a vote on whether they want them, because that would interfere with the Bangladeshis’ freedom of movement, and, if they have willing employers, their right to make private contracts.
Presumably, however, everyone would agree that by coming to America the Bangladeshis become subject to America’s laws. We’re not hypothesizing that they have extraterritoriality, or that they are subject to no law at all.
So: what if 150 million Bangladeshis vote to formally join Bangladesh to the United States as the 51st state?
After all, if the 150 million people of Bangladesh would benefit from the American system, and they freely agree that they would so benefit, why force them to move all the way here to get that benefit? Why not let them choose America as their country without leaving the home they love?
I presume (perhaps wrongly) that there would be universal agreement that the American people (or their government) would have some say in the question of whether Bangladesh becomes part of the United States. So why is it immoral for the American people to similarly have a say in whether the entire population of Bangladesh becomes part of the United States? Why, to turn Tim’s terms against him, is the question of where one lives the decisive one?