I defend nothing, I merely point out the conditions that created slavery.
When was slavery ever a compassionate institution?
When the alternative was death. Read some history, you know Greeks, Romans, Visigoths, Celts, Vikings, Persians, Chinese, Korean, Japanese, Aztec, Mayan, any tribe in Africa (then and now), Arabs, Souix, Apache, Iroquois, Tartars, Huns, Mongols,... do I need to go on?
Ah yes, a choice between death and eternal bondage and forced labor for life. Yes, I can see the compassion just dripping from the second half of that choice. </sarcasm>