Assume the truth of this doctrine, which no known human religion ever has taught: There is such thing as reincarnation. And, what's more, human souls can only be reborn as humans. But, that is all that is predestined -- there is no "karmic justice," it's all completely random, you might spend your next life as any human, in any part of the world, of any nation, sex, religion, ethnic group, or social class, you just don't know. (See Veil of Ignorance.)
Whatever optimizes your own chances for a happy and healthy existence in your next life under those circumstances, and in all your lives after that, that is social justice.
Whatever optimizes your own chances for a happy and healthy existence in your next life under those circumstances, and in all your lives after that, that is social justice.