Source:All major recent studies of immigrants indicate that they have a high labor force participation, are entrepreneurial, and tend to have specialized skills that allow them to enter under-served markets. Although it is a common misconception that immigrants "take jobs away from native-born Americans," this does not appear to be true.
http://www.lp.org/issues/immigration.shtml
It's difficult to see the above as anything but an argument in favor of the status quo.
We are given facts about the profile of typical immigrants under the existing immigration system in the USA. Does that tell us anything about the profile of typical immigrants under a system of open immigration?
Suppose Libertarians succeeded in converting some country to a Libertarian but democratic system of government. With open immigration, what would prevent lots of non-Libertarian immigrants from arriving and eventually voting the country back to a non-Libertarian system?
On the other hand, if Libertarians advocate unlimited immigration for Libertarians only, then wouldn't that make Libertarianism look bad? ("The platform of party X includes special privileges for people around the world who belong to party X. Become a member now because we might acquire power and you don't want to miss out on the special privileges. It's time for justice. Join the fight against the status quo of entrenched power and privilege!")
[Edited in an effort to make it more coherent.]