To my ear, arguments against immigration sound like rationalizations.  I suspect that most people simply oppose immigration whether or not they have a reason to oppose it.  So perhaps we need not a policy argument for nativism, but a psychological explanation.  If I had to explain anti-immigrant sentiment, I would tentatively explain it this way.

Jonathan Haidt, a professor of psychology at the University of Virginia, argues that conservatives score highly on their “ingroup” moral foundation in surveys.  The ingroup instinct leads us to identify with and subsume ourselves to a larger social group.  In tribal human society, this instinct must have been extremely important.  The prehistoric (and much of the historic) world was a constant war between and within competing bands, and in this world the protection of the group would have been critical.  One way to secure the group’s protection was to display absolute devotion to that group – tribal patriotism if you like.

Professions of ingroup loyalty continue in post-tribal society (e.g. Mike Pence calls himself “a Christian, a conservative and a Republican, in that order”).  Hopefully, most such claims are posturing.  But ingroup loyalties are fundamentally a commitment to treat similar people differently, according to their different group memberships.  At its extreme it leads people to simply turn off their moral intuitions when considering members of the outgroup.  Racists discount the rights of people of different races, fundamentalists discount the rights of people of different religious groups, and nationalists discount the rights of people born in different nations.  But whether the people in the outgroup are members of another race, religion, ideology, or nationality, applying a different moral standard to them is unjust.

Because people frequently interact with other races and religions in a liberal democracy, ingroup tendencies toward racism and religious fundamentalism are costly and unstable.  These biases have slowly collapsed as the groups intermingled.  Christian ingroup bias against Muslims might be used as a counter-example, but it is a weak one in historical context.  Such a bias is partially attributable to the small number of Muslims in America.

But by definition, Americans will not interact much with people from different nations.  It is easy to maintain a group bias against an outgroup that the ingroup will never meet.  A foreign outgroup has only limited recourse against domestic ingroup biases.  If they are denied the right to immigrate legally, foreigners cannot openly petition for their rights.  They don’t even have the meager protections of enfranchisement.  And the foreign outgroup will always be a small part of society because their children will assimilate toward the native ingroup.  Unlike racism and fundamentalism, nativism is electorally stable.

Progressives and libertarians score lower for ingroup sentiment than conservatives.  They tend to be more universalist in their moral outlook.  Although ingroup sentiment is important for survival in tribal society, I do not think it is morally defensible.  A universalist moral outlook must be correct – though no specific outlook is correct merely by virtue of being universal.  In encouraging conservatives to reject nativism, I am asking them to reject an immoral tribal instinct whose importance we have hopefully outgrown.