Unkay. As an atheist, I would agree with you. As a former Christian, I would quickly point out two things:

1) Things change, the Bible is a living document, which needs constant interpretation.

2) As Jesus said, we must live by the spirit of the laws. Therefore, it could be argued that God wasn't telling them to own slaves, he was telling them the proper way to deal with one of the day's acceptable practices.

However, I AM an atheist, so I kinda am waiting for a Christian's rebuttal.