You mention “It’s probably the case that the biggest harms from immigration come from people irrationally panicking about immigration, but (surprise!) people are in fact irrational.”.
From an EU-perspective, the effect seems pretty clear: After the refugee crisis 2015-2016 there have been numerous cases of populist right-wing parties gaining support or outright winning elections after running on anti-immigration platforms: to name just a few: the Lega Nord in Italy became part of the government, the FPÖ polled at their highest in 2016, and anti-immigration sentiment was at least influential for Brexit. These are arguably outcomes that substantially weaken political institutions and lead to worse governance.
This kind of backlash from some parts of the established population happens at moderate levels of immigration. We should expect it to be much stronger when immigration would be much higher under an Open Borders system, and account for the effects of that.
You mention “It’s probably the case that the biggest harms from immigration come from people irrationally panicking about immigration, but (surprise!) people are in fact irrational.”.
From an EU-perspective, the effect seems pretty clear: After the refugee crisis 2015-2016 there have been numerous cases of populist right-wing parties gaining support or outright winning elections after running on anti-immigration platforms: to name just a few: the Lega Nord in Italy became part of the government, the FPÖ polled at their highest in 2016, and anti-immigration sentiment was at least influential for Brexit. These are arguably outcomes that substantially weaken political institutions and lead to worse governance.
This kind of backlash from some parts of the established population happens at moderate levels of immigration. We should expect it to be much stronger when immigration would be much higher under an Open Borders system, and account for the effects of that.