From The Straight Dope:

This May 2000 Congressional Research Service Report (usinfo.state.gov/topical/global/traffic/crs0510.htm) describes human trafficking for prostitution and forced labor as “. . . one of the fastest growing areas of international criminal activity and one that is of increasing concern to the U.S. Administration, Congress, and the international community. The overwhelming majority of those trafficked are women and children. An estimated 1 to 2 million people are trafficked each year worldwide; 50,000 to the United States. Trafficking is now considered the third largest source of profits for organized crime, behind only drugs and guns, generating billions of dollars annually.”

Since trafficking is the third biggest illegal money maker behind drugs and guns, then if we use the logic of the Libertarian Party we should legalize slavery! That will reduce the profit motive in human trafficking and thereby reduce crime!