"We also know that law is made not for the righteous but for lawbreakers and rebels, the ungodly and sinful, the unholy and irreligious; for those who kill their fathers or mothers, for murderers, for adulterers and perverts, for slave traders and liars and perjurers---and for whatever else is contrary to the sound doctrine that conforms to the glorious gospel of the blessed God, which he entrusted to me" (1 Timothy 1:9-11, NIV).
Over the past few centuries, some have asked why a Christian would oppose slavery, since the Bible does not condemn it. While it is true that slavery exists in the Bible, it would be a mistake to suggest that it is never opposed. The issue is more nuanced and complex than it appears on the surface. Different conditions and situations existed in those days.
However, kidnapping and oppression never conformed to the teachings of Jesus Christ. He described a part of his mission as "to release the oppressed" (Luke 4:18, NIV).
As noted above, the slave trade was seen as contrary to sound doctrine (1 Timothy 1:9-11).
Jesus taught, "So in everything, do to others what you would have them do to you, for this sums up the Law and the Prophets" (Matthew 7:12, NIV). If I were a boy enslaved in Ghana, I would want to be rescued. If I were a young woman who had been kidnapped and forced into prostitution in Cambodia, I would want to be rescued.
Ultimately, Christians want to assist people in becoming free from Satan and sin by exposing everyone to the good news of Christ. Our opposition to slavery, oppression, and injustice compliments that objective in a profound way.