Well, lets give it a try.
Start with the basis for all social justice: We are all made in the image and likeness of God, and all life is precious and to be protected from its conception to its natural end. We tend to get into trouble when we let our politics gloss over aspects of this. Its impossible to have true justice when one group dehumanizes another, be it racism, slavery, abortion, embryonic stem cell research, euthanasia, pornography, etc.
We also tend to get into trouble when we call out one area of injustice and give the appearance of glossing over another, whether intended or not. Like if a bishop for example calls out a political leader visiting a church for a photo op, but stays silent on extremely a pro-abortion rights politician who speak sat a Catholic Church.