Vedanta basis for the golden rule

Swami Vivekananda held that, because we are one reality, if I hurt someone or cheat someone, I am injuring myself in a profound sense. Just as we take very good care of ourselves, we should take equally good care, if not more, of everyone else. The golden rule is – treat others as you would have them treat you. Variations of this phrase are found in every religion in the world. If you go to the United Nations Headquarters in New York, you will see this golden rule inscribed there. But now we know why is it that we should treat others the way we want them to treat us. Vedanta shows us how I and the other are not separate. This oneness of all beings is the foundation of morality.

-Swami Sarvapriyananda, What is Vedanta