These sentiments seem sort of silly. As a previous poster pointed out, the habitable world is covered by nation-states. Since it's not flags per ce, but rather, the notion of nationalism that people don't care for, the extensions of the argument is that people shouldn't have the right to live anywhere unless they agree with the concept. People constantly live under governments and societies where they do not share all values. The sentiment that leads people to say, "leave" is the very essence of the deep routed collectivist tribal mentality that people are objecting to. It more or less boils down to, you are either with or against us. It is similar to the view that opposition to a war implies sympathies for the oppossing side. Tribal instincts are so powerfully instinctually rooted that they often blind critical thinking, and create these destructive dichotomies.
From a moral point of view, I absolutely refuse to believe that a certain human being has more value, or deserves different basic rights based soley on where they were born or where they currently live.