Socialist economics part 2 (Communist economics)

In socialist economics, part 1, I raised some concerns with Frederik deBoer's definition of socialism. It behooves me to offer a more useful definition.

<tl;dr>
Marx tells us where we want to end up: "From each according to his ability, to each according to his needs." That is communist economics. But such a society comes only as a result of precursors:

In a higher phase of communist society, after the enslaving subordination of the individual to the division of labor, and therewith also the antithesis between mental and physical labor, has vanished; after labor has become not only a means of life but life's prime want; after the productive forces have also increased with the all-around development of the individual, and all the springs of co-operative wealth flow more abundantly – only then can the narrow horizon of bourgeois right be crossed in its entirety and society inscribe on its banners: From each according to his ability, to each according to his needs! Critique of the Gotha Programme ch. 1

So our task as communists, then is to begin to realize the precursors, to eliminate the "enslaving subordination" etc. I will label here as "socialism" the task of realizing the precursors, which will be the subject of the next post.
</tl;dr>

To understand socialist economics, I want to start with communist economics. Marx's "thousand year" goal is "from each according to his ability, to each according to his needs." A critical feature of this slogan are that a person's demand on the social product is coupled not to their contribution, but to their "needs". Marx can be vague about "needs" precisely because this is a goal, not a plan: part of the implementation of this plan is to more carefully define "need". Another critical feature, where I will again push back against deBoer, is that this definition does specify reciprocity: each person has the social obligation to contribute according their ability.

Marx does not believe that this slogan can be arbitrarily chosen or imposed on a society; he names a number of ideological and structural barriers, mentioned in the passage quoted above. I'll unpack this passage later; the question for now is not would this work? but is this worth striving for? And by "this" I mean not just the banner and slogan, but the precursors. Is it worth striving to eliminate "the enslaving subordination of the individual to the division of labor"? Is it worth striving to eliminate "he antithesis between mental and physical labor"? Should we strive to make labor* "life's prime want"? Should we strive to increase the productive forces, the "all-around development of the individual"? Should we make "all the springs of co-operative wealth flow more abundantly"? Communists answer these questions in the affirmative; indeed, if we have these precursors, the banner and slogan will naturally follow.

*I'll need to talk about Marx's conception of labor another time.

The question then becomes how to begin striving for a communist society, which brings us to socialist economics, the subject of part 3 of this series.