Why do you think a brilliant European should be allowed to work in America but not a brilliant African?
Or did you simply mean that rich, educated people should be given international mobility while poor, uneducated people should be content to rot where they were born?
I think he meant that infrastructure between first world countries is more or less integrated, and citizens are easily tracked and observable, so it should be theoretically easy and safe to have their mutual borders more or less open. Or something like that.
He didn't mention the poor, he mentioned people from the first world -- he may know the answer for people from a poor country, even if he does not agree with it.
Or did you simply mean that rich, educated people should be given international mobility while poor, uneducated people should be content to rot where they were born?