The question is raised in this post of Chris's. Along the way Chris wonders if exploitation is inherently bad. For my money, the word 'exploitation' when applied to relationships between persons carries a pejorative connotation. We use it to condemn the relation we're highlighting. For this reason, one needs either to avoid a definition of 'exploitation' that makes it neutral, a word to be applied in criticism in some cases and as content with a given state of affairs in others; or to purge the word of its normative content. I think it's easier to do the former than the latter.
Accordingly, the Marxian concept of exploitation should not be used without modification, if it is used at all. This is because Marxian-exploitation is - arguably - sometimes OK. Exploitation occurs in the Marxist sense when the 'fruits' of their labour are appropriated from workers by capitalists. In thinking as he does that this is exploitative and wrong, Marx assumes that the workers have a right to what they produce in the way of new value. However, as Chris notes, we do sometimes think that a proportion of one person's labour product may be used for the benefit of another, whether the first person agrees to this or not. Taxation for the provision of health care to those who need it is a form of appropriating the economic value produced by some and redirecting it towards others. If one thinks that this practice is justified, then it must be something else about the would-be exploitative relation between capitalists and workers that is objectionable than the appropriation, just as such, by some people of the value produced by others.
A Marxian-style concept of exploitation needs to be refomulated in terms of differential efforts and rewards, the unequal sacrifice of potentially free time, unequal suffering and enjoyment more generally - and, as Chris indicates, the way in which unequal wealth and power enable some people to take unjust advantage of others.
