Exodus 21:8 "If a man sells his daughter as a servant, she is not to go free as menservants do."
Although a rare practice, it was considered a parental right to sell one’s child as a slave. According to the law, a Hebrew slave would be set free after 6 years of service unless they decided to stay in the household as a slave (Deuteronomy 15:12–17).
But a man who bought a Hebrew girl as a concubine must commit to provide for her for life, sell her to another man who would provide for her as his concubine, or return the girl to her father without demanding payment for her (Exodus 21:7–11).
Deuteronomy 21:15-17 "If a man has two wives, the one loved and the other unloved, and both the loved and the unloved have borne him children, and if the firstborn son belongs to the unloved, then on the day when he assigns his possessions as an inheritance to his sons, he may not treat the son of the loved as the firstborn in preference to the son of the unloved, who is the firstborn, but he shall acknowledge the firstborn, the son of the unloved, by giving him a double portion of all that he has, for he is the firstfruits of his strength. The right of the firstborn is his."
What about divorce - that is a "moral" law?
In the first, Matthew quotes Jesus as saying: “It was also said, ‘Whoever divorces his wife, except on the grounds of porneia (sexual immorality), makes her an adulteress; and whoever marries a divorced woman commits adultery.” (Matthew 5:31-32).
Why aren't you spending your time railing against the evil of divorce and remarriage? Or buying girls as concubines?
God does not need you to be his policeman. "Let he who is without sin, cast the first stone." John 8:7 -said by Jesus to those who wanted to stone a woman for adultery. Your job is to care for other people, not loudly judge them. Jesus was absolutely clear on that. Why don't you take that verse to heart?
Your relationship with God is your job. Other people's is theirs. Mind Your Own Business and focus on your own sins. Those are the only ones that should actually matter to you.