A friend and I spend a Saturday night reading the Bible and the Koran a few weeks ago. It was fun and interesting. I have a lot to learn about Christianity and Islam. I wish I knew the entire Bible and Koran front to back. I'd apply them to all my arguments against their teachings which I learn more and more about.
In referring to slaves the Koran says that if a slave owner marries his slave's wife, then he must set his slave free. I thought that that was really nice of Allah, since it would be terrible for the male slave to now see his wife, former wife, now married to his owner. But the whole moral point to me is that Allah allows slaves in the first place.
The Koran just like the Bible justifies human slavery. It's interesting. I am still very new to the Koran and have yet to get into its details. As I learn more I'm sure there will be a few surprises.