Libertarians will argue that if we just get rid of the welfare state, then open borders will work. But this will not make the tragedy of the commons disappear, and people coming here will still be able to vote.
If libertarians aren’t going to argue that education is a human right that should be protected by the state in the absence of the complete privatization of everything, then they shouldn’t argue that free movement is a human right that should be protected by the state either. This isn’t to delegitimize the concerns that libertarians have with closed borders, but to instead show the many problems that exist with open borders. Hopefully libertarians open minded enough on the issue will begin to reconsider their position on immigration, and understand that open borders are not libertarian. Open borders are communist.