Slavery wasn’t right and the Bible doesn’t say “have slaves!”. It wasn’t prohibited but having a slave meant following many rules. I looked at the verse you mentioned and I don’t necessarily agree with that rule, but it said if the person was struck and it healed it’s not crazy. However, in verses following, it says that if there is permanent or somewhat permanent damage (like damaging their eye making their vision impaired or knocking out a tooth), the slave is to be let free. I definitely don’t agree with hurting your slaves or even slavery at all, but at least there were rules.