No, I don't support ethnic cleansing, and it's pretty sad that so many people on a supposedly socially liberal forum do. If, say, Catalan people vote to secede and create their own country, that's cool. But they shouldn't complain if non-Catalans start moving there.
And also, if the question was "Should languages and cultures be protected?" then the answer would be, of course they should. It's when you start forcibly removing people from their homes that it gets problematic.
By arguing against the existence of ethnically based states (or autonomous areas) you are de facto saying that smaller ethnic groups should be destined to become minorities in every country on earth.
Easy position to take if you belong to a large and dominant culture, but deeply discriminatory. There is an inherent paradox in that by saying every ethnic group should be equal everywhere you are de facto discriminating the smaller ones. Anglophone Liberals and leftists always seem not to understand this.
So we should fight racism with more racism? That's pretty horrible.