Rational and moral individuals would choose to be identified by the moral principles they claim to adhere to

If we are moral and rational beings, we must allow ourselves to be defined by the moral system we claim to subscribe to. Even nationalists must agree that what determines what is permissible to do for the purpose of promoting the national interest must be defined by morality.

It was Washington who said "Morality and religion enjoin good faith to all nations" and that "we must with caution indulge the supposition that morality can be maintained without religion." The New Testament is silent on this but the Koran has plenty to say on these subjects.

This is the only way the world can have nations convincingly claiming to have an ethical foreign policy which is  only way of avoiding war. If there is no justice, there will be no peace. 

Religion is intended to transcend race and nation. If we want to join a group, the religious group is going to be bigger than the nation in terms of numbers.