"The Bible however never condemns slavery so it's OK."

Way too simplistic. The racism-based slavery we think of today as slavery (excluding what we call modern slavery for a minute) was non-existent in biblical times. Slavery in the Roman Empire was a complicated setup in which you could be "promoted" or buy your way out. And just because "the Bible never condemns" this, that or the other doesn't mean it condones it. There is no mention by Jesus in the gospels of slavery but I would strongly argue that the sentiments contained in his teachings are at odds with the abuse and exploitation of fellow human beings. And I'm an atheist, thank God.