Southern Slavery and Natural Observation

What were the main arguments pro-slavery southerners used to defend the institution of slavery against accusations that slavery was barbaric and backward? What were the limits of these arguments (in other words, how were these arguments less than convincing)?

This is a natural observation study. For example at gym, you are observing women and men who exercise on the equipment. You notice that man exercise to build muscles and women just for recreation and they use less impact equipment. Hypothesis, tall sheet and graph. This is an assignment ONLY for psychology student or psychologist. It can be also about big dogs and men and small dogs with women in a dog park..