If we were to do away with the varying religions, we would find ourselves united and enjoying one great faith and religion, abounding in brotherhood. - Kahlil Gibran
While I doubt this is objectively true, that this would simply happen given our contradictory, selfish nature, this is what Karen Armstong is getting at with her Charter of Compassion. What is known as the Golden Rule is the underlying principle of all the world's major religious traditions. According to the ancient tale, Rabbi Hillel (in a time shortly before Jesus of Nazareth) stated that the heart of the law was "Do not to others that which is hateful to you." the rest of the law - he said - was commentary.
Artists such as Kahlil Gibran and John Lennon offered this observation to the world in various forms, whether through story, poem, or song. They asserted that the underlying notion of compassion for others is what is important, not all the extraneous dogmas the religions of the world pile on to it. In the 19th Century, Lew Wallace, author of Ben-hur, wrote a very long novel, The Prince of India, in which the protaganist seeks to reconcile the major world religions by showing how they are all based on the same philosophy of compassion. So the idea has been around for at least a couple hundred years, probably longer. I believe it speaks to the very passionate core of human beings, the need to identify and sympathize with others, and this is why it is so resonant. But, again, we humans are essentially self-contradictory. While we evolved the capacity for great compassion and charity for those in our tribe, we also developed the ability to practice cruelty and aggression towards those we see as outsiders. So, these yin and yang forces will continue to pull and prod at us, ultimately foiling our attempts to raise compassion on to a throne above us all.