First of all, social justice is based on concepts of human rights and equality. In a just society, everyone would receives the same rights and opportunities. Many countries are working toward that goal, but Canada or a few other counties in northern Europe may be one of the few that have almost reach this idealistic goal. Simple equality does not work in a society because there will be people who are more talented than others or who puts more effort into something. Therefore people who work hard deserve to earn some kind of reward. This process is normal, for when rewards exist, the system motivates people to work harder in order to obtain bonuses and those kind of rewards that are limited or special.
I believe the society is currently a mix of simple equality, equity, and merit (distribution theories). All of the theories are good if one makes good use of them. However, most of the time we see people use them in a negative way, abusing rules and gaining advantages upon others. There are no global written rules of what these theories are and what kind of behaviours is acceptable or unacceptable. When it comes to distribution, if we put the simple equality in use, every gets exactly the same amount despite different physical attributes. People with bigger physical ratio or mass may have bigger stomach and will need more food to convert to energy. What if one of the individual is allergic to the food or object we're distributing? What if the object as no use to someone? For example, we may be handing out a comb to each individual but one of them is bald. The comb would be useless for that person since he or she does not have any hair.
All in all I think all of the distribution theories must be put into coexistence. We must also fix this problem from the root-- teaching people, specifically, youth, to be just or incorruptible so that they would grow up into great adults. These adults would not merely take advantage of others but instead, serve others and if he or she knows that the object distributed is unnecessary for one own use, the individual would share it to others so that someone else that needs it will make good use of it.
In the end, it comes to Buddha's teaching of "staying on the middle path."