From Nations By Consent (pdf):

I began to rethink my views on immigration when, as the Soviet Union collapsed, it became clear that ethnic Russians has been encouraged to flood into Estonia and Latvia in order to destroy the cultures and languages of these people.

He goes on to describe “rethinking immigration on the basis of the anarcho-capitalist model”. I thought this was notable because the American context of the immigration debate can make it seem as if only nasty, right-wingers who don’t like dark-skinned people would question open borders. But here is Rothbard being led to question traditional libertarian thinking on this by something that I would think even left-libertarians would be sympathetic to… The plight of a people whose central state is using a “compulsory opening” to override the genuine wishes of the community and, indeed, to erase the distinctive community if possible.

The Best of Stephen W. Carson