I agree with all you say about the ambiguity of goodness, the ways in which we justify evil by appealing to a greater good, our tendency to develop narrow definitionsl of human community, and our bent toward selfishness. I even agree with your take on the golden rule.
Metaphors are always risky, but here's one I find useful. Think of the human story as a piece of music. All of the horrible themes we've identified comprise a major movement within the piece. At times the movement dominates, sometimes it recedes into the background, but it is always there. Still, it is not the only movement. There is another one, a second one, and it plays the great themes of an all-inclusive humanity, humility, sacrifice and deeply shared interests. The two movements play, contend, rise and fall--but they go on playing. Some of us hear one movement more clearly than the other; some of us hear only one theme. We often think we've mastered the music, though truth to tell no one ever really does. Still the music plays on, and neither theme is eliminated.
Now...in my view there is a Conductor who never ceases to try to bring the second movement to the forefront. This may well be the core difference between us. I don't know. In any case, though, I believe the Conductor is involved, though he operates within the limits set by the role he has assumed.
I choose to pay attention to the second movement, to allow its cadences and runs and pace and tone to become the music which is my life. I may well mishear a note, sing along off key, get out of beat--but so long as the second movement plays and so long as I try to listen, I ulitimately will be drawn back into the movement.
So I dare to sing or play or simply beat time to the second movement. So long as the second movement plays, I will not lose hope.