We had an open border policy thru Ellis Island for decades. Open in the sense of more generous than at other periods in our history. As opposed to the sketchy politically motivated quotas now that highly favor immigrants from the countries we helped to destroy. Open doesn't mean no screening for "means of support", disease, crime, corruption, etc. Under Libertarian policy, EVERY border crosser would HAVE to be a contributor, because all the "bennies" would go away. If they are attracted for the RIGHT reasons. Why not be generous?