Not every argument is supposed to be double-sided.
Mix-mashing all societies just get them to lowest common denominator. Similar societies usually receive similar outsiders. Sometimes even outsiders from same place. Which just makes them even more similar. For example, north Germany and Bavaria are quite different places and have different culture. Yet same set of immigrants come to both. Local food is different, but kebabs are the same.
If each society can choose who they want to accept and who they don't want... Then we can agree that each society can judge for itself.
Mix-mashing all societies just get them to lowest common denominator. Similar societies usually receive similar outsiders. Sometimes even outsiders from same place. Which just makes them even more similar. For example, north Germany and Bavaria are quite different places and have different culture. Yet same set of immigrants come to both. Local food is different, but kebabs are the same.
If each society can choose who they want to accept and who they don't want... Then we can agree that each society can judge for itself.