"Social justice" is a popular buzz word today that tends to create tension whenever it's spoken. But did you know the Catholic Church has an official teaching on what social justice is? At it's heart, Catholic social teaching is about making ethical decisions in civic, political and economic situations. It is not about welfare states or the abandonment of personal responsibility.
If you want to better understand social justice, listen to a voice that has seen governments rise and fall. Listen to the Church. A great introduction to Catholic social doctrine can be found in John Paul II's On Human Work (Laborem Exercens).