I see this debate as not really being about immigration, but as a facet of the eternal war between plutocrats and socialists. Plutocrats prey on socialist countries, exploiting their high standard of living and high social trust. Socialism more often than not arises when plutocrats have hollowed out a country and left it fallow, and interferes with the plutocrats second phase where they "brain drain" the now-desperate people and use them as shock troops in their next campaign. Plutocrats want to restrict immigration to the needs of business, while socialists want immigration to be as egalitarian as possible. As such, socialists and plutocrats are natural enemies. Socialist countries sometimes manage to shake off the plutocrats, and in fact America's "melting pot" idea was a well-timed inoculation against them.