As it happens, Doctor Who is right in the middle of a story about this. What's really surprising is that as of the first part of the story, Doctor Who seems to

As it happens, Doctor Who is right in the middle of a story about this. What's really surprising is that as of the first part of the story, Doctor Who seems to, for the first time ever, be taking a more right-wing than left-wing approach to the political metaphor. It turns out that letting twenty million shape-shifting Zygons settle on Earth actually was a terrible idea after all! Not all of them are bad, but a sufficient number are, and you can't tell the bad ones from the good ones. They'll probably find a way to twist it back to a leftism-compliant story in the latter part, but it's interesting that the first part of the story at least is a pretty convincing argument against letting large numbers of potentially-dangerous foreigners into your planet/country.