I looked up this passage. In the previous section it’s talking about releasing slaves who had sold themselves because of poverty. That the owners should do so in the year of Jubilee. This is a specific section that talks about people who want to sell their children to the Israelites when they’re already living among them. It’s a foreshadowing of the Gentiles being grafted into the kingdom of Israel. The focus is on the inheritance.
Philemon is about telling a master that he should release a slave if he considers what God has done for him.
Jesus fulfilled the law, so there are no more nations outside of Israel. Of course, you can twist the Bible to support chattel slavery after Jesus fulfilled the law. And it’s not surprising because we are sinful. Why do you suppose African Americans are Christians if they believe the Bible subjugates them?
Also, do you believe the world would be more moral without any belief in God? What principles would we base morality on? Doesn’t might make right today in many countries anyway?