Wm Abbott wrote:  "Slavery on the face of it is unjust. It violates the golden rule. The bible communicates the injustice of slavery magnificently. The abolitionist movement was distinctly Christian."

That the Golden Rule was being violated didn't abolish slavery. Slavery continued until there was political success in outlawing it—and against opposition from many claiming Biblical support. So, no, it is not true that "the doctrine of equality pursued politically has an unhappy history."