I am well aware of what Paul said and I also don't think he was endorsing slavery. You are saying that people's interpretation changes. The facts of the Bible haven't changed. Each is free to interpret as they wish. However, that doesn't change what God said or meant.
That was exactly my point and you are totally contradicts your original assertion that the bible is straightforward and easy to understand. The fact is that it is not as interpretations have changed in very major ways from one age to another.
Maybe your very literal interpretation of Genesis is wrong as was the interpretation the Paul endorsed slavery.