Social construct: an idea that has been created and accepted by the people in a society. Merriam-Webster Dictionary
The concept of "social justice" is not even close to being “accepted by the people of society”. Consider the following:
Social justice is a concept of fair and just relations between the individual and society. This is measured by the explicit and tacit terms for the distribution of wealth, opportunities for personal activity and social privileges. Wikipedia
Social justice is really the capacity to organize with others to accomplish ends that benefit the whole community…what is equitable is often not to give people the same portions, but rather to give what is proportionate to the efforts of each. Michael Novak/Heritage Foundation
As evident in the above quotations, disagreements about social justice often center on what is fair or equitable. And what one considers fair or equitable is partly based on whether a person's allotment is deserved - that is, earned by virtue of personal qualities or actions.
Deservingness isn't just about what a person is or does, though. It's also about the broader social and economic context: the rules of the game that dictate which qualities or actions are rewarded. If there's something wrong with the game itself - say, it's rigged to favor those with power, connections, or the "right" skin color - then game winners don't deserve their spoils. At least that's the logic I encounter a lot on the left, e.g.,
“[S]ocial justice requires...the eradication of existing forms of social oppression. Social justice entails a "redistribution" of resources from those who have "unjustly" gained them to those who justly deserve them…” Joe R. Feagin, "Social Justice and Sociology: Agendas for the Twenty-First Century: Presidential Address"
It's no accident that political arguments about social justice tend to focus on the role of hard work versus luck. For instance, in a recent Pew Research Survey, 73 % of Solid Liberals agreed that “hard work and determination are no guarantee of success for most people”, compared to 4% of Core Conservatives. That's a huge difference. No wonder the partisan divide has turned into a chasm. The disagreements are on so many levels: bickering turtles all the way down.
Next: The Psychology of Social Justice continues: perceived control and reactions to successful people.