Whenever the topic of Marx or Marxism is broached around economists, or graduate students studying [bourgeois] economy, they immediately launch into ideological invectives that not only demonstrate an utter ignorance of the Marxist canon - an ignorance passed off as intelligence - but an ignorance of what they think is "wrong" with the Marxism: the labour theory of value.
I'm tired of arguing with people who have no bloody idea exactly what the labour theory of value is. These are the people who immediately launch into tirades about how Marx "misunderstood price" or that there is "something called supply and demand."
No shit. There is also something called actually reading Marx, and everyone who rejects the labour theory of value is either: 1) an utterly stupid idealist who believes that the economy is some sort of natural force outside of human existence (the invisible hand); 2) someone who misunderstands (either intentionally or because they haven't done the reading) this "labour theory of value."
Of course it doesn't help that so many people who are pro-LTV are geeky Marxist economists who get lost in economic-speak, fascinated with how Marx used the LTV to describe price, etc. So what is this strange beast called the Labour Theory of Value?
I think Rosa Luxemburg did a good job of summing up the LTV in The Accumulation of Capital: "It is of course true that raw materials, instruments, and the like, must be taken into consideration with all labour. Yet is it not true also that these raw materials and instruments in their turn are equally the products of labour [...] We may go back as far as we choose, we may twist and turn the problem as much as we like, yet we shall find no element in the value of any commodity - and therefore none in the price - which cannot be resolved purely in terms of human labour." (The Accumulation of Capital, p. 36)
Without human labour a commodity would not possess a market value. Without humans to work and make things that will be exchanged, then there would be nothing to exchange. The LTV ultimately means nothing more complex than value comes from human labour. Yes, we can imagine machines making things on an assembly line but: 1) human labour was responsible for the creation of these machines; 2) human labour maintains these machines.
Looking at it on a more philosophical level, though, we can say that the concept of value itself is intrinsically connected to human existence. We produce value by saying what is of use to us, what is more valuable than something else, etc. Without humans there would be no "value" as such. Without human labour there would be no exchange-value: if nothing was made than nothing would be exchanged.
So idiots who claim that the LTV is wrong ultimately believed that value originates in some source other than human. Do things possess some sort of eternal value determined by the heavens? Where does value come from? Supply and demand? Are these natural forces that are not dependent on human action? Did they exist before humans and thus will exist for all time? Of course, the bourgeois economist and the students of bourgeois economy will never answer these questions: they will just blather on about some inane model that they have imposed upon existence, not a model (like dialectical materialism) that is derived from real existence. This is why Samir Amin called pure economics a "parascience [that] compares to social science as parapsychology compares to psychology. Like any parascience it can be used to demonstrate anything and its opposite." (Spectres of Capitalism, p. 140) Amin also points out that the bourgeois economic institution enlists "amateur mathematicians" that can use "mathematical terms to throw dust in the eyes of non-mathematicians." (ibid., p. 142) He compares it to a modern witchcraft that, like the occult practices of old, believes in invisible market forces and uses esoteric terminology to justify the status quo.
People who don't believe in the Labour Theory of Value are idiots.