I've said a lot in the archives, but something more succinct may be said.
We know that the left likes to discount or even deny the moral difference between doing and allowing harm. "Social Justice" is the term they use to do this. Justice really has to do with harms one person does to another; it is something like the state in which such harms are not done or are punished and corrected when they are done. "Social justice" is the state in which no one is well off while allowing anyone else to fare poorly, either everyone faring poorly or everyone faring equally well. This makes it an injustice a person to be wealthy while anyone is poor, making it irrelevant that the harm of poverty was not created by the wealthy person, making it his crime that he allows it, and thereby doing away with the moral relevance of the doing and allowing harm.
That's a big mistake. And here's why. Morality is such that grave injustices tend to override other moral considerations. To enslave or impoverish another person is a grave injustice. It would need remediation very urgently. Considerations of honesty, procedural justice, loyalty, and even the duty not to cause harm would tend not to stand up against it. The Underground Railroad was morally upright, after all. It was permissible to lie to free a slave, to be disloyal to free a slave, and even to do violence to a slave master who refused to free his slave. It is also permissible to take property from a wealthy person who has stolen it from someone else and thereby impoverished that person. Robin Hood is, after all, a hero, not a villain. This is all, at least roughly, as it should be. But when "social justice" replaces ordinary justice, we run into trouble. The left makes redistribution of wealth (from the wealthy who obtained their wealth fairly and to the poor who are poor through no one else's doing) more important than considerations of honesty, procedural justice, loyalty, and even the duty not to cause harm. This is why the left is dishonest, scoffs at the rule of law, shrugs at considerations of loyalty, and doesn't mind harming innocents in order to try to bring about an egalitarian society. This is how progressivism has been so destructive to American political life.
An aside: It's the true believers I'm referring to here. Some of the leaders are merely opportunistic kleptocrats or power-hungry narcissists who care not one whit about moral considerations. You can't always tell which kind of leftist you're dealing with. Barack Obama said that he didn't like the Constitution because it left out "positive rights" (another term for "social justice") and he is happy to violate the Constitution and to follow Jonathan Gruber's advice that Americans be lied to in order to get them to accept Obamacare. Wilson was happy to take political prisoners. FDR was happy to pack the SCOTUS with six more justices in order to get his New Deal control of people's economic lives. Are these true believers or merely opportunistic kleptocrats or power-hungry narcissists? Perhaps a mix of both, as the soul of man is complex.