For me, Marx goes off the rails with the binary notion of “socially useful” labor. Labor is not either useful or not useful. Labor is of varying social usefulness. The laborer pays the capitalist to identify for the laborer (by offering the highest wage) the most socially useful labor the laborer can do.

We can see an extreme example in this joke:

2 guys on the road. One was digging a hole , the other one waited a minute and filled the hole back up. Then they moved on and after about 10 feet they did the same — digging up , waiting a minute , and filling it back up. They went on doing this the whole morning, covering almost 3 miles of land. One guy who was watching them eagerly just couldn’t resist any more, and asked — are you guys mad or what ? What the hell are you doing ? The guys replied. We are from the government Forest department. We are a three guy team. My job is to dig up a hole, another guy plants a tree, and this guy fills the hole back. The middle guy called out sick today.

The labor of the two guys who show up is “socially useful” almost entirely because a third guy shows up to plant a tree. Whose idea was it to put hole-diggers and hole-fillers to work in a way that is socially useful? Standing alone, neither skill is very valuable. Even together, a digger and a filler do no “socially useful” labor. But the synergy of interposing a tree planter, who might not even be a person — maybe it’s a machine — makes the others’ labor socially useful.

The value of the planted tree does not come from the amount of time spent by the laborers; it comes from the time spent by the capitalist first preparing to figure out and then actually figuring out that hole-digging and hole-filling could be made socially useful by sticking a tree in the hole, from finding the tree, selling the contract and recruiting the digger and the filler. The laborer is not a supplier. The laborer is a purchaser of social utility from the capitalist, which the laborer repackages as labor and resells at a profit to the capitalist. So, who’s exploiting whom?

And thus it is for all of the capitalist “exploitation” of labor. The fact is that there is no such thing as “socially useful labor.” There is only labor, and its value comes from how socially useful it can be made to be by someone who gets paid for doing just that.