Here is a very good piece by The Mitrailleuse, though I do not agree with all of it. Here is the conclusion:
In summary, the libertarian discussion surrounding immigration shouldn’t be viewed as an all or nothing proposition and as Sanandaji has argued, it should take real world empirical patterns into account rather than assume away voting, the public sector, and social externalities. Libertarians should adopt the same skeptical economist’s view they apply to all other subjects when weighing questions about immigration to determine if we can actually affect the changes we would like to make.
It is perfectly acceptable for libertarians to disagree on such a complex subject and to hold opinions in favor of more marginal change. There are plenty of modest ways libertarians can criticize the existing immigration system without being in favor of open borders. These libertarians shouldn’t be vilified for their humility and prudence. There is no academic consensus on the subject and the issue is too complex and contextual for there to be a clear-cut libertarian position. The burden of proof lies on advocates of open borders to engage these criticisms.
For the pointer I thank Andrea Castillo.