Do you believe that Paul had authority to teach in the name of Jesus? If you do, then you have to conclude that Jesus is pro slavery, because Paul certainly is.
In Paul’s letter to Philemon, he sends back the former slave Onesimus who had run away. Paul does NOT tell Philemon to take the slave back as a slave but as a brother in Christ. And then he follows up the strong suggestion with an announcement that he’ll be coming to see Philemon.