If you want to live in a homogeneous society I’m sure you can find one where you’re happier. The United States has been multicultural since the beginning. The fact that the founders, all of them immigrants or descendants of immigrants, didn’t think through the consequences of mass-importing slaves and realize that at some point their descendants would live free in the country where they were born is not the fault of anyone alive today, but we can never become a country of a single ethnic group because we never were to begin with.