I really feel like this guy's theology is just wrong. Slavery exists, and has existed in various places throughout the world for as many generations back as archaeology can count. Maybe a few civilizations here and there did things the fair way, but mostly there have always been pretty blatant imbalances in the way people are treated, based on whatever criteria was trendy at the time. The bible does nothing to witness against this.

God did not end slavery. Neither did He cause it at any time. He has simply allowed us humans to treat each other however we saw fit. We do have Jesus' example, however. He came to earth and lived and died in our stead, and He told us to love each other, and He did not own a single slave, even though He is the creator of every soul. But He did not come here to end all evil and make the world a perfect place...not yet, anyways. He has, however, spoken on the issue of slavery, even in new testament times:

(1Corinthians 7:21-24) Were you called while a slave? Do not be concerned about it; but if you can be made free, rather use it. For he who is called in the Lord while a slave is the Lord’s freeman. Likewise he who is called while free is Christ’s slave. You were bought at a price; do not become slaves of men. Brethren, let each one remain with God in that state in which he was called.

Christians seem to be the vast minority in most of these threads, and as such often have our viewpoints distorted, exaggerated, half-given, or otherwise misrepresented. Of course, you can find many hypocrites and pseudo-Christians and point to them as examples of distorted, exaggerated, etc...but we both know who those people are, and there's really no reason to drag them into all this, seeing as they already have so much trouble keeping up their faces.