In slavery, the ones in pain are actually the product.
There is a voluntary exchange between the buyer and the seller.
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And it's a fine example of how the efficiency of the market has nothing to do with the 'goodness' of the situation.
This is why science isn't about morality. It would be interesting to see some of these "free marketers" become products themselves. They might provide interesting data.
We would first have to argue that slaves are not people; if slaves are not people, we have no right to call slavery immoral, for one cannot abuse an object lacking its own subject (i.e. damaging someone else's things e.g. it's fine for a person to damage their own property as the subject is okay with this, but wrong to damage another's unless that subject is okay with that; the slave, assuming it is property, has no subject of its own, ergo is not a person.)
If slaves are people, then we must assert that there is a subject involved who does not participate in another's voluntary exchange; if the individual agrees to slavery, he is not a slave (though he may play the role willingly; maybe he's into that), and if the individual does not, then he is being denied his right to his subject and, hopefully, none will agree that this is the righteous path and subsequently help him (sadly, this has hardly been the case considering the past several thousand years.)
Either way, slavery cannot exist within a free market. There is no situation in which slaves are both people and involuntarily participating within a free market; this is a logical fallacy. Either the slave is a person to which the slave-owners are wrong and the involuntary trade should be abhorred, or the slave is not a person therefore cannot be considered amongst other human beings as to whether the trade is good or bad for it, just as trading an iPad for however many BTC cannot involve ethics applied to either the iPad or the money, as they have no subject of their own.
The latter can never fit within the realm of ethics because we generally recognize slaves as human. What we apply to one human, we must apply to another, as we otherwise develop a divide between which groups have rights and which groups do not (i.e. the state and its citizens), which presupposes that there are multiple groups of human beings when there is only one, as Occam's razor shows us. The latter can only be achieved without human empathy (in which case every individual has their own moral category), but we cannot assume this is the norm, especially among people who bring up slavery as a good example of why free markets are not necessarily right or wrong (this implies slaves are considered people, otherwise it'd be as strange as bringing up a PS3 in this regard, and nobody would understand what was meant.) We see here that it is illogical to place slaves in their own moral category, as morality, the very foundation of law, becomes null if people can simply decide when morality will apply to them, and when it will not. Assuming we do want a society of order, then we must adhere to the idea that all people have equal rights; without this, there can be no free market, as there is always a subject, even if they are
treated as property, who participates involuntarily, thereby revealing the authority figure necessary for regulated markets thus making the free market void to give way. This does not mean that every crime nullifies the free market, but it does mean that every crime legitimized shows there are regulatory powers at work: they cannot coexist.
Ergo, for a market to be considered free, it necessitates all subjects claim ownership over their objects, i.e. ownership of their being, their time and energy, and the product of their past efforts, otherwise we are left with objects without subjects, to which other subjects claim ownership i.e. authority, even if temporarily (the core idea behind the regulated market); because there can be no involuntary trade within a free market, every trade is always to the benefit of the individuals involved, otherwise the trade would never occur; following this logic, we can also see that every trade made involuntarily (or trades disallowed by ulterior forces) are to the detriment of the subjects involved, as it steals or suppresses either the subject's time, their personhood, or their property, or all of it. Even the situation in which a man trades his life and wealth for poison is beneficial for each party as they both get what they wanted (but of course, the man cannot trade his wife or children as this implies they have no subject when they do.)
Anyway, ethics is a science insofar a person understands it; to make a comparison, merely because a person believes 2+2=cupcake does not mean the concept of mathematics is a farce or otherwise inapplicable, it simply means the person isn't versed in concepts of math, and merely because the individual who believes 2+2=cupcake asserts that math is not a science for he can find no constants related to the universe does not mean the constants are not there. It doesn't stop him from doing so, of course.
