> So you're saying that the net positive migration from countries like Sweden to countries like the US is due to the fact that generally only relatively successful people have the ability to immigrate? And that if all classes of society were able to move freely that the net migration would be in the other direction?
Yes.
> Do you have any evidence to support this claim?
I don't. Just a lot of anecdotal evidence from a life spent living in different European countries and U.S. states, talking to people and learning about their lives.
I do think that logic follows that a society with both a high standard of living and high equality would be a more attractive target for a low-income earner than one with a high standard of living but high inequality, but I am unsure if this means that, for example, Americans would actually want to emigrate to Sweden if they didn't know much about it. There are still a lot of misconceptions about what "socialism" means in Europe, how much freedom the U.S. has and Europe doesn't, and so on.
(I think that this is part of the reason that, if true, the U.S. sees more traffic from Europe: The entire Western world grows up with American movies, TV, songs, etc., but many Americans don't know very much about Europe other than that they used to be the HQ of nazis and other socialists. But yes, it's just speculation.)