I am surprised that libertarians think people can protect their own rights but not a whole country. Some libertarian philosophers I have  a great deal of respect for. But in this subject they seem to be off. If a hostile population is intent on invading Europe and the USA, why should the borders be open? After all a country is made up of people. If people can protect their own right and space so also a whole group of people ought to have the same right. I don't invite jihadists into my home. Why should a country invite them into its boundaries?

And this does not just mean physical boundaries. Every group has laws and norms. In the Talmud we find that to become Jewish there are standards. That is to keep the laws of the Torah. There is a whole formal process that this involves. No anyone can get in the front door. And even after you are in the front door there are standards. This is so in any group. Whether it is the Jewish people, or the Army or Marines. You certainly don't let people in that openly claim to want to break down the country or group.