This thread seems to be a particular instance of a general tendency to quote biblical passages that one finds troubling and then criticize the Bible/God/Christianity for what one finds troubling. Not that anyone here needs my help, but I’d like to jump right in anyway because this is an interesting subject.
First, although the point is almost universally lost on contemporary atheists (e.g., the 4 horsemen), all religious texts are borne from particular religious communities. These texts do not stand on their own, and they are not the equivalent of perspicuous articles in The Economist magazine, which just anyone could pick up, read and interpret quite apart from the community. I myself would never presume to pick up the Quran, read it by myself and then go tell the Muslim what it means (or the Mahabharata or a Koan, and on it goes). If I’m outside of the religious tradition, I will go to the tradition to try to find out what
they say it means. This approach to religious texts and practices seems so obviously to be the only rational approach that I continue to be boggled at the presumption of some atheists in their handling of the Bible. It is a bizarre and too often repeated practice. Perhaps @Mike_from_NJ here is not doing this, but it certainly comes across that way.
Second, not all slavery is created equal, as has been argued by others above. A good piece of scholarship that illustrates this is
Slavery and Social Death: A Comparative Study.
Third, I take the following to be a moral principle that would be universally adhered to: the dehumanizing mistreatment of anyone is abhorrent (a gross moral wrong). If it could be established that all forms of slavery/servitude throughout all times and in all places have been instantiations of dehumanizing mistreatment, then it would follow that it is and has always been a moral wrong. But, that would first have to be argued for. The book I cite above argues against that suggestion. Not all varieties of slavery/servitude are created equal. Some have been much worse than others.
Fourth, I think in objections like Mike is raising there is an underlying assumption of what might be called an existential approach to freedom, like Sartrian “absolute freedom” (or maybe a Nietschean “will to power”). There seems to be a presumed belief here that humans are and should be entirely free. But, whatever freedom humans have is constantly constrained, limited and hemmed-in from all sides. This is the condition in which we persist. Absolute freedom is myth which could never be realized by creatures such as humans. Who among us does whatever she wants whenever she wants it? No one. Whatever freedom we enjoy (say, as a middle-class contemporary Westerner) is deeply constrained, conditioned, limited, hemmed-in…