There are many ways to isolate a country without resorting to xenophobic political isolationism. Geographic isolation works, for one. Even if you do use xenophobia, you can give a nod to the consequences, or just show your point of view characters at least aware it's not a perfect system. Not whole stories of it; just passing mentions here and there. It's not hard, and only focus-damaging to the fringe minority who cling to the empty fantasy of fiction being entirely divorced from the world of its reader.
Quite frankly, if you can't imagine anything better than creating a system that needs to legitimize (both in the sense of justifying, and in the sense of presenting it as without negative consequence) extreme xenophobia to keep its focus...you don't have enough imagination in the first place,to be a good witer.
Good witers don't need that kind of crutches to keep their focus where it needs to be.
Edited by Himoto