While I said similar things in my earlier post (that the framework for exploitation, such as in the case of labour, to occur does not exist, at least always, in BDSM relationships), I want to revisit a point in response to the above: I am not sure how you would define exploitation... does it require both an 'exploited' and an 'exploiter'? For there are cases where only the former exists. Why is it that a person desires masochistic experiences? It is possible that it may be an exploration of the opposite by an otherwise dominant person. It is also possible that a person who was abused as a child seeks out similar treatment, perhaps to their psychological detriment. What is mostly clear to me is that one cannot pass blanket judgement on such sexual sadism or masochism as reflective of psychological imbalance. History and biology (not to forget the cultural development of a individual) suggest that we have multiple, complex tendencies built into us and in the case of sadism perhaps such consensual play provides a safe outlet (even converting a negative into a positive) than does denial of such desires. However, with a masochistic person, it seems to me that special attention is to be paid to the cause of her or his desire (not just a release form signed in triplicate). If I am right, where and how is such care taken? Just as feminism has taught us (inter alia? ;-)) the imbalance of power in historical male-female [sexual] relationships and the special attention to be paid to the woman's experience of it, it behoves us to more closely examine the consent (from the masochist's perspective) issue and not just provide caricatures of certain phrases of certain feminists ("all sex is rape" etc).
Andie made a post recently on this matter and an earlier post of mine reflected (anticipated?) his point regarding the burden of proof. I think those of us posing questions about SM need to take that burden seriously, though I do believe that we are (or should be) speaking here of colloquial proof, not formal proof. I hope my tentative thoughts above are a step in that direction.
--ravi
P.S: of course the roles of sadist and masochist are possibly reversed/reversible in such experiences, perhaps even within the same experience/event, so the above has to be further constrained, at least in the interest of terseness, to ignore such.