I think you have cut through a lot of smoke with your summary of the "marxist" concept of justice. Now, in order to put it forward as definitive, it seems to me that one has, at the outset, to excommunicate a good part of the "marxist" community (say, for example, "marxists" within the liberation theology movement), but "marxists" are very good at excommunications, so this should present no particular obstacle.
I am interested in your summary as it relates to "marxists" who will remain within the fold after this distinction is made, those who adhere to a strict materialism, and deny out of hand the existence of any moral absolutes.
My own favorite discussion of this is Kolokovski's. I think he shows rather well that one of the central difficulties arising from this form of fully materialistic "marxism" is that it does not allow for a reasonable answer to the question, why should one be a "marxist," a revolutionary, or what have you?
In my own philosophical dialogue with my father (an unrepentant "marxist" of nearly 90 years), this issue has, I would say, been fundamental. In all these years, I have never heard a convincing explanation from him as to why he devoted his life to revolution. Of course, for him, it is easy to explain why he is a marxist. After all, marxism is scientifically correct. That's self-evident.
Well, to him it is.
I really wish that he had expressed his philosophical position on justice as simply as you have. At least that would have been more honest. Instead, I got nothing from him but beatings about the bush. On the other hand, he did set me down at a very tender age to read Trotsky's "Their Morals and Ours," so I can't say that I didn't get the message anyway. Ultimately, I came to my own conclusion, which is that, at the center of my father's view of the world, there is a spiritual black hole. I was close to falling into the hole myself, before an unpredictable variable skewed my orbit, freeing me from all that sucks in philosophy.
Think of this: I know my father to be the kindest individual I have ever met in my life. Yet, if he were put forward as a candidate for political power, I would have to rise and say, "Please beware. Please don't." Even kind men can be cruel. Tolstoy asks such a simple question in "Resurrection": would a judge sentence a man to death if he had to cut his throat personally? My father the man, would not raise a hand against anybody. My father the "marxist" would sign the appropriate papers and retire to his study to read another book.
Quincy