Unintended consequences

One of the worst blights on humanity is the continued existence of slavery. In his book "Discover Your Inner Economist: Use Incentives to Fall in Love, Survive Your Next Meeting, and Motivate Your Dentist" Tyler Cowen has the following example of one attempt to deal with the suffering associated with it,

Nicholas Kristof, a reporter at the New York Times, had a novel idea for how to reduce suffering. He got on a plane to Cambodia and decided to buy and free two slaves. It cost him $150 and $203, respectively, to free each slave, plus of course plane fare and expenses. The girls were, most likely, otherwise destined to lives of prostitution, rape and quite possibly AIDS. A number of charities have been buying and freeing slaves in Sudan.

This sounds, and is, virtuous, but is it the answer to slavery? On a large scale there is a danger with such a policy. If we buy out a large number of slaves we bid up the price of slaves. This makes slavery an even more profitable business to be in than it already is. Which is not what we want. Any increase in the profits from slavery would lead to even more victims becoming enslaved. It may mean that a given person is a slave for a shorter period of time but more people would becomes slaves for that shorter period. This honest and well meaning attempt to deal with the problem could be counterproductive, we may end up with a bigger problem than we started with.