The correct answer is 4) The Constitution seemed to support it.
The option that was not an argument used by Southerners to defend the institution of slavery was "The Constitution seemed to support it."
The Southern States used every argument they had at hand to defend the use of slaves in the plantations. Indeed, the Southern States depended so much on slavery to grow crops that could be exported, Slavery was part of their economy. The cited Biblical passages, social arguments, historical facts, and political issues to defend their arguments over the accusations of the Northern states.
