It's generally considered unsound because it relies on the labour theory of value -- that "true" value comes from the labour expended during creation of a good.
That was the state-of-the-art in classical economics when Marx branched from it. And his argument flows from it.
But the LTV breeds paradoxes. That's why, when the concept of subjective value was introduced, economics left LTV behind.
A thing is only valued according to what it is exchanged for.
So a single good actually has different values, at different points in time and space. The value of the labourer's efforts are a distinct exchange from the value of the good to the manufacturer, which is distinct again from the value when sold to the wholesaler, distinct from the value at the retailer, distinct from the retailer to the consumer, distinct again the value between the buyer and the buyer's son who inherited it, distinct again to the value at a lawn sale, distinct again to the value at a swap meet, distinct again to the value at a recycling centre ...
There was no "real" or "true" value to be expropriated here, so the Marxist critique basically falls to pieces. It continues to be attractive because it makes sense to people who are unaware of more modern economics, because it predicts cyclical behaviour in capitalist economies and because it finishes with some hand-wavy eschatological futurism that sounds really pleasant.
That was the state-of-the-art in classical economics when Marx branched from it. And his argument flows from it.
But the LTV breeds paradoxes. That's why, when the concept of subjective value was introduced, economics left LTV behind.
A thing is only valued according to what it is exchanged for.
So a single good actually has different values, at different points in time and space. The value of the labourer's efforts are a distinct exchange from the value of the good to the manufacturer, which is distinct again from the value when sold to the wholesaler, distinct from the value at the retailer, distinct from the retailer to the consumer, distinct again the value between the buyer and the buyer's son who inherited it, distinct again to the value at a lawn sale, distinct again to the value at a swap meet, distinct again to the value at a recycling centre ...
There was no "real" or "true" value to be expropriated here, so the Marxist critique basically falls to pieces. It continues to be attractive because it makes sense to people who are unaware of more modern economics, because it predicts cyclical behaviour in capitalist economies and because it finishes with some hand-wavy eschatological futurism that sounds really pleasant.