Why does God condone slavery?

[localroger]

39. As a practical matter, civilization such as it was could not have existed without slavery

I have read that there were a couple of times when it was suggested to make Roman slaves wear an identifying mark or special clothing, but it was realized that there were so many slaves that if it became too easy for them to identify one another it would actually make rebellion easier. The invention of agriculture pretty much necessitated the co-invention of slavery, and while modern technology has finally made it theoretically possible to separate the threads of civilization and oppression the habit of oppression is now so ingrained that it has proven to be a hard one for humans to break, whether in the form of actual or de facto (e.g. wage) slavery.