Many libertarians are for open borders but there has been a large shift in the last couple years.  Hans-Herman Hoppe is probably the one of the most well know Austrian economists that has contributed to this shift.  From an purely economic point of view open immigration makes sense, after all, free trade is a good thing.  If we believe in the free movement of goods across borders why not people? Hans- Herman Hoppe has countered this that a group of have the right to associate with who they want and that also means that they have the right to not associate with who they want.  This is a basic natural right.  My views have shifted to the Hoppe view.  Moving whole groups or cultures into a civiliation ate a rate that is impossible to assimilate is a fools errand.  This is made increasingly worse with the modern welfare states, this puts a drag on the whole system and consumes a great amount of resources.  This is what is happening to Sweden today and this has become one of the best examples.  The video below explains.