I don't think public policy decisions should be affected by the economy anyway. We don't want Congress trying to be a chef for the economy and saying one day, "Needs some more immigrants," and another day, "needs less immigrants," like they're ever gonna tweak it the right way.
I see basic ethical principles behind this discussion that don't change with the economy. Speaking of that, let's set aside the abstractions about culture and demographics and wishful thinking about what a country should look like. What exactly do those who think the government's role includes preserving some culture or demographics think it should be doing? Do they really think it's ok for the government to make employers tell them who all their employees are and make sure they have the government's permission to work here?