Well, ethnicity is literally the Greek/Latin word for a tribe and a tribe is defined by the people within it by any standards they choose, so that's why I have no issue with the idea of ethnic states on principle even though it can be done wrong in practice and used to justify all sorts of heinousness. Also, using the word "ethnic" to refer to groups that aren't multicultural is completely ridiculous and basically frames multiculturalism as a new religion. America is a multi-ethnic state and you can tell this because people identify themselves as things like Irish, German, English, African and Asian more often than just American, while the idea of American ethnicity tends to refer to people in the South. People in England with English citizenship almost always consider themselves English even if they're black, same with people in Germany and Hungary and many other European countries, but people in favor of forced multiculturalism want to paint ethnicity as being something that's closed for most people just to load the term with racist connotations. Granted, it's not easy to become a black Brit or Middle Eastern German but it's not easy to become an American immigrating from Mexico either even if the Mexican-American will probably keep their expatriate (another loaded word) ethnicity while the Brit and German won't. But then, I also had a German teacher who considered herself "more American than German" so ethnic identities in America are just messy in general.

https://en.wikipedia.org/wiki/Ethnic_group