However, this argument does say that labor exploitation in a country that has prohibited it is wrong because it conflicts with the laws set by that society. Such exploitation is unnecessary and serves only to enrich the employer at the cost of the worker. Furthermore, it competes with societies that are trying to better themselves. To support such endeavors is indifference at best. For some it is also spitefulness against the rules of society.
Now there are some labor exploitation practices that are universally wrong. The CIA World Factbook lists 32 countries where human trafficking and slavery are practiced with the authorities doing little about it. Another less obvious form of slavery is debt bondage or bonded labor. A person either pledges work as security for a debt or has a debt that they are trying to work off. In either case the person cannot leave until it is repaid. Sometimes these debts are inherited. Other times the people are forced to also work off their room and board which is set at a price higher than their "salary". The BBC website reports that perhaps 20 million people live under such conditions.
Knowingly supporting such practices is obviously wrong. There are, however, some ethically grey areas. For example, it is common knowledge that diamonds are sometimes mined through such illegal practices. Yet most diamonds on the market today are relatively old and in some cases have been worn for centuries. To say that one will never wear a diamond because brand new ones might be ill-begotten is probably being over-ambitious. For a woman being offered an engagement ring, she could easily do more harm than good by rejecting it. For those who have made such a boycott a focus in their lives, the issue could be avoided by ordering a diamond in advance with instructions that its previous owner is verifiable.