Once again, you ask a question that you know perfectly well is misleading and inaccurate. I’m frankly surprised at you, @josie, as you are a much better thinker than this. Questions of this nature ought to be beneath you. Nevertheless, I will point out things of which you are already aware for the benefit of anyone you might be fooling with your dishonesty.
First, there is no such thing as the current version of social justice theory. People who are interested in what is sometimes referred to as “social justice” have various views about what precisely this entails, and the topic is approached from a variety of philosophical viewpoints. There is not even a single “progressive” notion of social justice. To pretend that it is a monolithic enterprise, then, is simply foolish.
Second, no particular theory of social justice holds that everyone in disadvantageous circumstances is there in virtue of having been victimized by a system. Nor does any theory of social justice deny that individual failings may lead a person into an unfavorable condition. The question is what to do about it when such situations arise: how far, and how hard, ought we allow people to fall?
It is in the early stages of addressing this question that we find the most overlap in theories of social justice, and in which we find the kind of statements your question so blatantly misrepresents. That is to say, most theories of social justice start by recognizing the existence of moral luck: we are born into a world without an even playing field—something that surely cannot be our own fault—and there’s not much that can be done to change that.
Given that it is neither possible nor desirable to ensure equality of outcome, then, those interested in social justice are typically interested in exactly how we might have meaningful equality of opportunity. If you ask a dog, a fish, an elephant, a penguin, and a monkey to climb a tree, you’re going to get different results. You can claim the test is fair in virtue of being the same for everyone, but this is a rather thin and unsatisfying notion of fairness.
This is the point Rousseau makes in his political works about the fact that the mere act of setting up a society is already one of picking winners and losers. All institutions involve a structure in which some talents are placed above others, and this decision is more artificial than we typically realize from our perspective within the system. Since the social contract is meant to be for the benefit of all, however, something should balance this loss.
Theories of social justice can accept the existence of class differences, and they can accept that those who are “stupid, ineffective, incompetent, and/or worthless”—whether absolutely or just relative to the structure of society—will not be at the top of whatever hierarchy exists. What social justice theorists tend to argue is just that those at the bottom should not be forced to a life not fit for human beings—especially if they are on the bottom merely because someone has to be. For that is a clear case of moral luck.