"From this aspect, therefore, the whole of economics can be reduced to a single lesson, and that lesson can be reduced to a single sentence. The art of economics consists in looking not merely at the immediate but at the longer effects of any act or policy; it consists in tracing the consequences of that policy not merely for one group but for all groups.
Nine-tenths of the economic fallacies that are working such dreadful harm in the world today are the result of ignoring this lesson. Those fallacies all stem from one of two central fallacies, or both: that of looking only at the immediate consequences of an act or proposal, and that of looking at the consequences only for a particular group to the neglect of other groups.
It is true, of course, that the opposite error is possible. In considering a policy we ought not to concentrate only on its long-run results to the community as a whole. This is the error often made by the classical economists. It resulted in certain callousness toward the fate of groups that were immediately hurt by policies or developments which proved to be beneficial on net balance and in the long run." Hazlitt, Economics in One Lesson
The last paragraph, I think, really demonstrates the difference between the social justice theorists and the Miseses and Rothbards, etc. The social justice theorist sees the short-term, but cares little to none about economic realities and consequences.
“The revolt against reason, the characteristic mental attitude of our age, was not caused by a lack of modesty, caution, and self-examination on the part of the philosophers. Neither was it due to failures in the evolution of modern natural science. The amazing achievements of technology and therapeutics speak a language which nobody can ignore. It is hopeless to attack modern science, whether from the angle of intuitionism and mysticism, or from any other point of view. The revolt against reason was directed against another target. It did not aim at the natural sciences, but at economics. The attack against the natural sciences was only the logically necessary outcome of the attack against economics. It was impermissible to dethrone reason in one field only and not to question it in other branches of knowledge also.”
This is from Mises, Human Action, ch.3
This is what I came to realize not too long ago. He goes on to argue that Marx had to come up with the “bourgeos economics” idea because he could not counter the arguments and refutations of his earlier ideas in Das Kapital, etc.