Well I oppose the free entry of individuals into the US as to do so would be quite insane. Most immigrants do not enter the US with the intention of obtaining welfare. Once they get here and find out how easy it is to get then they sign up. I do not blame the immigrants for obtaining it either, I blame the government who gives it to them.
But that is quite beside the point. The free entry of persons would end this country as we know it in short order. There are BILLIONS of people around the world who be here tomorrow if they could and not for the welfare. How long would you stay in Pakistan if you could get to and stay in the US?
Remember what happened when Carter indicated that he would not deport people arriving from Haiti. Now imagine that on a planetary scale and you would see what an open border policy would result in. This country would resemble Bangladesh or India within a year. Crime and civil war would shortly follow.
I agree with a few positions of the libertarians but as long as this is in their platform they lack all credibility and can't be taken seriously.