The reason you are having a hard time understanding these points is because you genuinely don’t believe that nation states should exist. You may not think this explicitly, but that is the logical conclusion of the moral/ethical haranguing you are doing. What are you expecting as an acceptable counter argument here? Someone to develop the justification of the nation state from first principles? Your argument is that there is a universal principle of equality which disallows countries discriminating in favor of their own citizens. This is unworkable because the whole point of the nation state is to discriminate in favor of its own citizens.